Glossary

Please select term by "A-Z" or by "Category".

Abscess

An accumulation of pus within body cavity following tissue breakdown. Abscesses may be found in the deeper skin layers, the dermis or subcutis, and may either be sterile or contain bacteria. Treatment generally includes antibiotics, surgical drainage and lavage. Pus accumulation within the superficial layer of skin, the epidermis, is called a pustule.

Acantholysis

Loss of cohesion (binding) between epidermal cells. Separation of cells may result in clefts, vesicles and bullae. Seen in inflammatory, viral and autoimmune diseases especially pemphigus complex.

Acanthosis

An increased thickness of the stratum spinosum layer of the epidermis. May result from either increased size of cells (hypertrophy) or increased number of cells.

Acetate Tape Preparations (adhesive tape stripping)

A diagnostic procedure which enables direct sampling of the surface of the coat or skin. May be used to examine hair or skin cell structure, ectoparasites or other micro-organisms. Limitation is that the technique only provides a sample of the skin surface. Technique: Adhesive tape strips may be applied to either clipped or unclipped coat. A commercial clear adhesive tape is pressed onto the skin surface of a sample area. Strip is removed, stained with a Romanowski stain (a sequence of fixative, eosinophilic dye, and basophilic dye) and laid across a glass slide for microscopic examination.

Acne

A chronic inflammatory disorder. Canine acne is a localised form of deep pyoderma , also called muzzle folliculitis or furunculosis. Signs are more commonly observed in young, short-coated dogs, possibly secondary to trauma, and include sterile papules which develop into a suppurative folliculitis or furunculosis following secondary infection. Serous or purulent exudate and ulceration may be present. Comedones are rarely seen in canine acne. Treatment is dependant on lesion severity and may include topical antimicrobial therapy or a systemic course of an appropriate antibiotic where secondary infection has developed.

Acral lick granuloma

Skin disorder in dogs caused by licking of localized area of skin. Usually seen on lower limbs especially carpal or metatarsal regions. Initial cause may be behavioural but skin trauma and secondary infection may increase pruritus, resulting in greater licking of area.

Acute Moist Dermatitis

See pyotraumatic dermatitis.

Adrenal function tests

Specific diagnostic tests which may be used in the diagnosis of disease of the adrenal glands. The adrenal glands are two small glands which are located just cranial to each kidney. Each gland has two distinct sections. The medulla (inner section) of the adrenal gland secretes the catecholamines epinephrine (adrenaline) and norepinephine (noradrenaline). The cortex (outer section) has three functional zones, secreting: (1) mineralocorticoid (aldosterone), (2) glucocorticoids (e.g. cortisol) and (3) androgens and oestrogens. Adrenal disease may result in either increased or decreased production of adrenal hormones. The most commonly used adrenal function tests are those used to assess the adrenal cortex function. Over production of corticoid hormones is called Hyperadrenocorticism (Cushing's diseaese). Under production is called Hypoadrenocorticism (Addison's disease). Frequently used tests include the adrenocorticotropic hormone (ACTH) stimulation test (also called corticotropin test), low dose dexamethasone suppression test and high dose dexamethasone suppression test.

Adrenal tumours

Tumour or neoplasia within the adrenal gland, a small endocrine gland located cranial to the kidneys. The adrenal gland consists of 2 major components. The adrenal cortex (or outer structure) is responsible for production of endogenous steroids or hormones which control glucose metabolism (glucocorticoids) and mineral and water homeostasis (mineralocorticoids). The adrenal medulla is responsible for the production of the hormone adrenaline, the "fight-flight" hormone. Tumours of the adrenal gland may affect one or both of these structures. An example of a disease which may result from a tumour of the adrenal cortex is Hyperadrenocorticism (Cushing's disease).

Adverse food reactions

Includes food hypersensitivity or allergy , toxic food reactions and food intolerance. Food hypersensitivity is a non-seasonal pruritic skin disease of dogs associated with ingestion of allergen in the diet.

Allergen

A substance that is capable of inducing an allergic reaction. Examples include pollens, mites and flea saliva.

Allergen avoidance

Avoidance (or removal) of substances known to generate a hypersensitivity reaction in an individual (allergens). Common examples in canine dermatology include flea control (flea allergy dermatitis), elimination diet (food allergy), removal of allergenic plants from environment (contact allergy), and insect repellents (insect bite hypersensitivity). Some allergens are ubiquitous in the environment (such as house dust mites, pollens, mould spores) making avoidance an impractical treatment or diagnostic option.

Allergen avoidance

Avoidance (or removal ) of substances known to generate a hypersensitivity reaction in an individual (allergens). Common examples in canine dermatology include flea control ( flea allergy dermatitis ), elimination diet ( food allergy ), removal of allergenic plants from environment (contact allergy), and insect repellents (insect bite hypersensitivity). Some allergens are ubiquitous in the environment (such as house dust mites, pollens, mould spores) making avoidance an impractical treatment or diagnostic option.

Allergen-specific immunotherapy (immunotherapy)

A treatment used for management of atopic dermatitis (also called hyposensitisation, desensitisation or allergy vaccines). Treatment objective is to reduce the incidence of future flares and the requirement for additional medications. Immunotherapy must be preceded by allergy testing (intradermal skin testing or serological IgE measurement). Solutions are formulated to contain a combination of identified allergens, tailored to suit the animal's individual allergy profile. The solution is administered via a series of (usually subcutaneous) injections. Dose and frequency of injections is adjusted depending on patient response. The exact way in which immunotherapy works is unknown. Theories have included desensitisation of antibody or cellular reactions, induction of 'tolerance' of allergens, or formation of reaction-blocking antibodies. Results may be observed after about 3 - 6 months (some report longer), and regular boosters are required.

Allergic threshold

Animals which have developed a hypersensitivity reaction to an allergen may have an immune response to low levels of allergen without displaying clinical signs of disease. As allergen exposure levels increase, the animal will start displaying clinical signs of disease such as pruritus, erythema and inflammation. The level of exposure at which the animal begins to display clinical signs is called the allergic (or pruritic) threshold. The allergic threshold may be lowered if, for example, a dog is hypersensitive to house dust mites and is also infested with fleas. Management of allergic skin disease is often based on reducing allergen exposure to a level below the allergic threshold (e.g. elimination diets) or increasing the threshold (e.g. Immunotherapy and barrier treatments).

Allergy testing

Testing for the presence of a hypersensitivity reaction to a specific allergen. Testing may be based on measurement of response following direct exposure to the allergen (e.g. intradermal testing, provocation trials) or the presence of an allergen specific immunoglobulin (IgE) in the blood stream.

Alopecia

Loss of hair coat either due to failure to grow or breakage or shedding of grown hair.

Alopecia X

Castration responsive dermatosis, "woolly" syndrome, hypogonadism. A sex-hormone related skin condition affecting male dogs. Affected dogs develop hair loss (alopecia) of the trunk if the condition is secondary to testicular atrophy, or of the perineal and inguinal areas spreading forward to the ventrum and trunk (slow maturation). Initial signs are subtle and may occur over several months, with dogs first losing their primary or guard coat. The residual secondary coat gives the dogs a soft, puppy-like appearance. This coat then becomes dull and crimped giving dogs a "woolly" appearance. Hairs become lighter before gradually being lost. Diffuse hyperpigmentation of skin may or may not be present. Testes are often normal on palpation, but may be small and symmetrically atrophic. No other physical abnormalities are detected. Age of onset varies but generally occurs in dogs over 2 years of age.Cause is unknown. br/>Diagnosis is based on ruling out other endocrine disorders such as hypothyroidism and hyperadrenocorticism . Other differentials include testicular neoplasia, adrenal sex hormone imbalances and follicular dysplasia. Castration with histopathology of the testes may be diagnostic and signs may also improve within 4 months of surgery. Treatment: Castration results in improvement in a large percentage of dogs. Failure to improve warrants investigation for adrenal hyperplasia-like syndrome. Trial therapies with melanin (or if unsuccessful, testosterone) have been reported.

Anagen

Part of the cycle of hair growth. Anagen describes the period of active production from the hair follicle. On epilation the root or bulb of the hair appears smooth, rounded and shiny with or without pigment. A normal haircoat generally has a combination of hairs in anagen and telogen (inactive) phases. Catagen (intermediate stage) hairs are less commonly observed.

Anal Sac Disease

Anal sacs are two blind pouches located on each side of the anus between the internal and external sphincters. The walls are lined by secretory sebaceous glands and sweat glands. Secretions, a strong smelling blend of fatty and sebaceous materials and cellular debris, are released from each anal sac through a fine duct. A small amount of this material is normally expressed when the dog defaecates. Diseases include impaction (most common), infections (secondary to impactions), abscesses (following infection), and neoplasia (see perianal tumours ). Small breed dogs are most commonly affected, with the cause of disease unknown. Some factors may predispose to anal sac disease such as obesity or intestinal disorders like diarrhoea. Impacted sacs (or blocked ducts) may need to be expressed several times, generally about 1 week apart. If signs don't resolve, anal sac irrigation may be required. Infected anal sacs are expressed where possible, or ideally flushed (lavaged) under anaesthetic with lactated Ringer's solution. Antibiotic solution or cream is then instilled. Process may be repeated after about one week. If recurrence of signs then surgical removal of anal sacs may be required. Abscesses are treated under anaesthesia. Lesion is opened by surgical incision, infected contents are removed with a curette and topical iodine solution applied. Lesion is then left open to heal by granulation. Failure to heal or repeat episodes are an indication for surgical removal.

Angioedema

A vascular reaction of the skin usually marked by the sudden appearance of large areas of painless swelling (oedema) in the subcutaneous tissue or submucosa which tend to leak serum or display haemorrhage. Lesions may or may not be pruritic and are caused by mast cell or basophil degranulation. May occur as part of an immune based reaction (such as Type I or Type III hypersensitivity), following psychological stress, or physical stress (temperature extremes, sunlight, exercise, pressure) or in response to certain drugs and chemicals. Individual wheals may resolve within 24 hours but urticaria may be either acute or chronic. Differential diagnoses include cellulitis (juvenile or infectious), and neoplasia (such as mast cell tumour). Diagnosis is based on history, presentation and identification of trigger. Prognosis depends on location (angioedema of nasal passages, larynx or pharynx may be fatal). Treatment includes elimination or avoidance of trigger, epinephrine and/or glucocorticoids.

Antibiotic

A drug used to treat infections caused by bacteria and other microorganisms. Antibiotics were first identified when it was noted that some microorganisms seemed able to inhibit the growth of others. While original antibiotics were derived from these microorganisms, synthetic versions are now available (often chemically related to the natural substances). Antibiotic drugs have a characteristic mode of action on target micro-organisms. The mode of action dictates the types and structures e.g. of bacteria, against which the drug is effective (often referred to as the 'drug spectrum'). Bacteria are loosely grouped into four categories: Gram positive aerobes, Gram positive anaerobes, Gram negative aerobes and Gram negative anaerobes. Selection of an appropriate antibiotic should ideally be based on idenfication of the bacteria via culture. Susceptibility to the selected antibiotic may then be confirmed with sensitivity testing (checking for the presence of drug resistance). Often antibiotic treatment is started while awaiting these results. In these cases (or where culture and sensitivity testing is not an option) drug selection may be based on the most likely causative organism (eg Staphylococcus in pyoderma ), or a broad spectrum antibiotic may be administered. Antibiotics may either be applied topically (for example for surface skin, conjunctival or corneal lesions) or administered systemically. As systemic drugs are carried to the site of action via the blood stream, ability of the drug to reach the site of infection should be considered. Activity of the antibioitic in the face of pus, etc should also be considered.

Antidepressants

Anything used to treat depression, particularly drugs used for this purpose. The major groups of drugs available include tricyclic antidepressants, serotonin reuptake inhibitors, monoamine oxidase inhibitors.

Antifungal

A drug used to treat fungal (yeast or mould) infections. The term can be used to describe any drug that destroys or prevents the growth of fungi. Antifungals may be used as topical treatments or given systemically. Systemic treatments are generally required for systemic mycoses, subcutaneous mycoses and often for superficial dermatophytosis. Topical formulations include creams, lotions, shampoos and rinses. major drug categories include azoles ( eg clotrimazole, miconazole, thiabendazole), chlorhexidine, nystatin and amphotericin B, naftifine and terbenifine. Systemic medications used include griseofulvin, the azoles (imidazole, ketoconazole, itraconazole, enilconazole, fluconazole, triazoles), amphotericin B, flucytosine and terbinafine.

Antihistamines

Drugs that combat the histamine released during an allergic reaction by blocking the action of the histamine on the tissue. Antihistamines do not stop the formation of histamine, or the interaction between the antigen and IgE. As such antihistamines do not stop the allergic reaction but offer protection against some of the effects of histamine release. Histamine is only one of the many molecules that causes pruritus & inflammation in dogs. Examples of antihistamines used in dogs include chlorpheniramine maleate and trimeprazine. Use of some antihistamines in dogs may be extra-label.

Antiseborrhoeic

A treatment used for management of an oily scaliness of the skin, termed seborrhoea . Strength of agent varies and should be selected based on severity of the condition. Listed in general order of increasing potency of product: Sulphur and salicylic acid shampoos Pure tar products Tar combination products Benzoyl peroxide +/- sulphur products, selenium sulphide shampoos. Use of strong tar products or those of greater potency may increase water loss through the skin. These products should be used cautiously. After-treatment with a cream rinse or emollient may help reduce this drying effect. Mix shampoo with a small volume of warm water prior to application to increase distribution and reduce the likelihood of skin irritation at site of application. Shampoos generally need to remain in contact with the skin for 10 - 15 minutes prior to rinsing to have an effect.

Atopic dermatitis

A genetically predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features associated with IgE antibodies most commonly directed against environmental allergens.

Atopic-like dermatitis

An inflammatory and pruritic skin disease where signs are identical to those of canine atopic dermatitis but an IgE response to allergens cannot be confirmed.

Atrophy (epidermal)

A decreased thickness of the deeper (non-cornified) layers of epidermis generally due to a reduction in cell size. May be seen in dogs and cats in hormonal disease (such as hyperadrenocorticism ), developmental disease or, rarely, inflammatory disease (e.g. discoid lupus erythematosus).

Aural haematoma

Bleeding of blood vessels within the pinna (or ear flap) resulting in a localised pocket of blood forming in the subcutis. The degree of swelling may range from a small area to the entire surface of the pinna. Initial bleeding may be caused by self trauma such as vigorous head shaking which may occur as a response to the presence of pruritic skin disease such as otitis externa, parasites (fleas, ticks , mites ), or allergic skin disease (e.g. atopic dermatitis). Treatment generally includes surgical drainage and compression of the haematoma and treatment of any underlying cause. Where no obvious physical cause of ear or skin irritation is present, blood clotting disorders should be considered.

Autoimmune reaction

An immune response formed by the body against its own cells or tissues. The immune response may be directed against a single cell type, or against multiple tissues. Autoimmune reactions can result in either localised or systemic illness due to cell destruction. The cause or trigger of the immune response is often unknown, although potentially some toxins, heavy metals, medications or microbial infections may initiate a self-targeting reaction.

Autoimmune skin disease

A group of skin diseases where cells or tissues are destroyed by the body's own immune system. Skin disease may be part of a multi-systemic disease, depending on whether a single cell type or multiple tissues have been targeted. Autoimmune diseases tend to occur more frequently in older animals, the underlying aetiology is generally unknown. While these diseases are comparatively uncommon, some of the more frequently reported autoimmune skin diseases or disease groups include: Pemphigus complex, bullous pemphigoid, lupus erythematosus , cutaneous adverse drug reactions , erythema multiforme and cold agglutinin disease.

Azoles

Antifungal medications which may be used in the treatment of dermal mycoses ( fungal skin disease ) such as Malassezia or dermatophytosis. Members of the 'azole' family are metabolised via the cytochrome p450 pathway (primarily in the liver). Consideration should be given to potential interactions with other medication metabolised in this way (e.g. cyclosporin) or which may potentiate metabolism. Azoles may affect endogenous cortisol production and liver function should be regularly monitored during therapy. Use in animals may be extra-label.

Bacterial folliculitis

A bacterial infection of the hair follicle. This may be divided into superficial bacterial folliculitis and deep bacterial folliculitis. A superficial bacterial infection is contained within the superficial part of the hair follicle. This may be a primary lesion (such as following trauma, or poor grooming) or secondary to other underlying disease (e.g. seborrhoea, allergies, parasites, endocrine disease, or dermatophytes). Primary lesions may or may not be pruritic. Disease can progress to become deep folliculitis, furunculosis or cellulitis . Signs include: inflammatory papule then pustule around a hair shaft, crusting, epidermal collarettes , hyperpigmentation , excoriation , alopecia. Diagnosis involves observation of primary or secondary skin lesions and elimination of other potential follicular pathology by skin scrapings (mites), hair examination or fungal culture, and cytology of exudate. Investigation for an underlying cause is important particularly in recurrent cases. Treatment includes administration of an appropriate antibiotic course and addressing any underlying disease. Deep folliculitis and furunculosis result from rupture of the follicle or progression into the deeper skin layers. Deep folliculitis generally results from trauma or progression of superficial infection. Aggressive antimicrobial treatment is generally required.

Bacterial skin disease

Many bacteria are normal inhabitants of the skin surface. Bacterial skin disease results when the skin barrier is impaired or damaged such as by trauma or underlying disease. Bacterial disease may be either a primary condition or secondary to other systemic or skin disease. Some animals may also develop a hypersensitivity reaction to a bacterial antigen (e.g. Staphylococcus intermedius ). Bacterial skin disease is generally pruritic and is classified and treated based on depth of infection, causative organism, and the presence of underlying disease. Depth of bacterial infection within the skin ranges from surface infection ( pyotraumatic dermatitis , body fold pyoderma ), superficial infection ( impetigo , superficial pyoderma, superficial folliculitis ), deep infections (localised deep folliculitis and furunculosis , generalised deep pyoderma, cellulitis and mycobacterial infections) to subcutaneous ( abscess , mycoses , Nocardiosis).

Baker's biopsy punch

A disposable skin-punch biopsy instrument. The punch biopsy can be used to collect a skin lesion sample for histopathology. A 6mm punch generally provides an adequate sample. Smaller punches may be used in difficult biopsy sites (e.g. near the eye).

Basal cell carcinoma

A less common neoplasm (tumour) of the skin originating from the basal layer of the epidermis. Tumours generally occur in older animals, and are more commonly found on the head, neck and thorax. Tend to present as single, well-circumscribed, rounded lesions with localised alopecia, are often highly pigmented and may be ulcerated. Treatment ranges from observation to surgical excision.

Behaviour-modifying drugs

Drugs used to modify an animal's behaviour. These may include, for example, anxiolytics (anti-anxiety), antidepressants , anticonvulsants and tranquilizers. These drugs may be considered in skin disease characterised by self destructive behaviour, abnormal licking or chewing and pruritus where a significant component of the cause is thought to be psychological.

Biopsy

Removal of body tissue for examination, generally under microscope. Biopsy method may vary with location, size and type of lesion. Biopsy types may include impression biopsy (or smear), impression biopsy (smear) fine needle aspiration, needle biopsy, punch biopsy , incisional biopsy (removing section of lesion) and excisional biopsy (removal of entire lesion).

Blepharitis

Inflammation of the eyelids. May occur with localized irritation to the eye or as an extension of skin disease elsewhere in the face or body.

Body fold dermatitis

A form of Intertrigo, a surface bacterial skin disease caused by friction between opposing folds of skin. Increased humidity in the skin area potentially predisposes to infection. Breeds with pronounced skin folds (e.g. English bulldog, Shar pei) may be predisposed. Intertrigo also occurs on facial folds, lip folds, vulval folds and tail folds.

Bowen's disease

A form of neoplastic skin disease considered either an early stage or intraepidermal form of squamous cell carcinoma.

Calcinosis cutis

Calcium salt deposits within the skin. Localised lesions may occur secondary to trauma. Widespread calcium deposits are seen with hyperadrenocorticism , or rarely ventral deposits may occur due to penetration through the skin of calcium carbonate (limestone) or calcium chloride. With hyperadrenocorticism lesions are often seen around the dorsal neck, rump, and axillary and inguinal regions. Initially lesions appear as firm, whitish papules or plaques. Skin then becomes inflamed leading to redenning, ulceraton and crust formation. Diagnosis is based on history (environmental exposure, or signs consistent with endocrine disease), appearance of lesions and investigation for hyperadrenocorticism if suspected. Treatment involves avoidance of environmental calcium sources (for dogs with ventral penetration lesions), or treatment of underlying endocrine disease ( hyperadrenocorticism or 'Cushing's disease').

Candidiasis

Infection with the Candida species of yeast. As the Candida species may be found normally in many parts of the body, infection is usually opportunistic. Immunosuppression or damage to the skin barriers may predispose to infection. Infections in the dog most commonly occur in the mucocutaneous junctions (as malodorous, non-heaing ulcers) or in high moisture skin areas (ears, folds, feet and claws). In skin, the lesions appear as papules or pustules , becoming erythematous oozing plaques and ulcers. Lesions are extremely pruritic. Differential diagnoses include intertrigo or bacterial skin disease (for skin lesions) or immune mediated disorders for mucocutaneous lesions. Treatment involves management of underlying disease or cause of skin damage, and appropriate antifungal therapy.

Canine juvenile cellulitis

A rare condition generally affecting puppies aged between 3 weeks and 4 months. Condition is generally painful but not pruritic. Golden retrievers, Dachshunds and Gordon setters may be predisposed. Clinical signs: Initially swelling to the face (eyelids, lips, muzzle) and enlargement of local (submandibular) lymph notes followed within 1-2 days by papules and pustules appearing particularly around the eyes, lips, muzzle, chin, and bridge of nose. Lesions deepen into fistulae which drain and crust. Ears often develop pustular otitis externa with the pinna becoming thickened and oedematous. Puppies may appear systemically unwell with signs such as lethargy, joint pain, and pyrexia (fever). Involvement of the subcutaneous fat cells (panniculitis) results in sterile pyogranulomatous nodules forming under the skin (may feel firm or fluctuant and be painful or fistulate). Differential diagnoses are angioedema or allergic reaction. Diagnosis is based on history and presenting signs of facial swelling combined with regional lymph gland enlargement +/- systemic signs. No microorganisms are found on cytology (sterile, non-parasitic). Treatment: Early and aggressive glucocorticoids until disease is inactive. Systemic antibiotics if secondary infection has developed.

Catagen

Part of the hair growth cycle. Catagen describes an intermediate phase between the active growth (anagen) and follicle inactivity (telogen). On epilation, the root or bulb of the hair has an appearance midway between that of anagen and telogen hairs. The normal haircoat generally consists of hairs in either anagen (active growth) or telogen phase. Intermediate catagen hairs are less commonly found.

Cellulitis

A severe deep bacterial skin condition characterised by the acute spread of infection below the skin surface. Bacterial infection may occur due to progression of superficial infections such as folliculitis or furunculosis or may be introduced by trauma (self-trauma, bite wounds etc). The deep infection is poorly contained and spreads laterally through the subcutaneous tissue. Clinical signs include erythema (redness), heat, oedema (swelling) and pain. Depending on the cause, the overlying skin may become friable, darkly discoloured and, if devitalized, sloughing may occur. Enlargement of local lymph nodes and pyrexia may also be observed. Causative bacteria may either be aerobic or anaerobic, in both cases aggressive antibiotic therapy is indicated. Anaerobic cellulitis lesions tend to be more severe and spread more rapidly. Potential sources of infection include puncture wounds, bite wounds, or foreign body introduction. The wounds may have a putrid odour and if gas-producing bacteria are present the skin may feel crackly on palpation (crepitus). Production of toxins by the causative bacteria may result in systemic signs. Surgical drainage and lavage, and removal of necrotic tissue is also indicated in these cases.

Cheilitis

Inflammation of the lips.

Cheyletiella

A surface living species of fur mite of dogs, cats and rabbits. Potential for transmission to humans (zoonosis). Movement of the mite through the fur has earned the title "walking dandruff". Diagnosis is through demonstration of the mite in skin scrapings or acetate tape preparations.

Chiggers

Also known as harvest mites or trombiculid mite.

Coat brushing

May be useful for identification of flea faeces, fleas or Cheyletiella in the coat. An easy test with an immediate result, but does not sample the skin surface. Technique: Animal is supported on a hard white surface (such as table) or over white paper. A fine tooth comb is run through the coat rapidly, or for small animals the animal is balanced on their hind limbs and one hand is rubbed through their coat. Hair and debris that fall to the surface are examined under magnification. Small streaks of blood appearing on damp white paper placed on the debris is positive for flea faeces ('flea dirt').

Colour Dilution Alopecia

An inheritable condition that tends to occur in dogs which have been bred for a diluted form of coat pigment i.e "blue" (dilution of black and tan colour) and "fawn" (dilution of red or brown colour gene). The condition is characterised by progressive loss of haircoat resulting, eventually, in widespread permanent hair loss. Not all blue or fawn coloured dogs are affected and the mode of inheritence has not been clearly identified. Affected dogs are usually born with a normal coat. Changes in coat may be seen from as early as 6 months of age (those with lighter coloured coats) or as late as 2-3 years of age (darker blue coats). Initial signs are generally seen on the back (dorsum) and may include dry skin, hair loss, or a recurring bacterial infection (folliculitis). Infection of the hair follicle is seen as small bumps in the skin. Antibiotics may improve the signs of infection, but haircoat regrowth is slow or non-existent. Hair loss has generally progressed to include all light coloured areas of the body by 2-3 years. Darker (e.g tan) coloured points are not effected. Exposed skin may appear scaly. Diagnosis is generally through ruling out other potential causes ( demodex mites or endocrine disorders such as hypothyroidism ), then microscopic examination of plucked hairs ( trichogram ) or skin biopsy. Under the microscope, affected hairs have larger, unevenly distributed pigment granules (macromelanosomes). Clumping of melanin rather than uneven distribution may occur in non-affected pale coat dogs so confirmation is often on biopsy where follicular dysplasia may be observed. No known cure, but the disease should not otherwise affect the health of the dog provided symptomatic support of the skin is implemented. Treatment includes moisturising or emollient solutions, sun protection (no longer protected by haircoat) and antibiotics for skin infections as required. As the mode of inheritence is not clear, breeding from affected dogs, their parents or siblings is not recommended. Also called colour mutant alopecia, blue or fawn Doberman syndrome, fawn Irish setter syndrome, or blue dog disease.

Comedo / comedones (pl)

An accumulation of keratin and sebum within the opening of the hair follicle. Also called a "black head". Often contains bacteria. May be seen for example in feline acne or in Cushing's disease (hyperadrenocorticism).

Conjunctivitis

Inflammation of the conjunctiva of the eye. May be caused by trauma or the presence of a foreign body such as grass seed, infectious disease or systemic disease. Depending on lesion cause, one (trauma or foreign body) or both eyes may be affected. Conjunctivitis may be accompanied by inflammation of other tissues of the eye such as cornea or eyelids.

Contact allergy

Also called allergic contact dermatitis and contact hypersensitivity. A rare skin condition generally affecting lightly haired areas of skin. As compared to a primary contact irritation, the disease results from a type IV hypersensitivity reaction. Clinical signs include a varying severity of dermatitis in hairless or sparsely haired areas of skin (ventral paws interdigital region not pads), ventral abdomen and thorax, tail, neck, scrotum, point of chin, perineum, and lateral pinnae. With chronic disease lesions may spread. A history of slow spread would be reported in these cases with expanding hair loss at the edges of pruritic, reddened (erythematous) areas of skin. More heavily haired areas of skin could be affected if the allergen is in liquid, aerosol or powder form. Site of lesion may indicate potential allergen source (e.g. nose and lips for allergen in food bowl or chew toy, neck area for collars). Primary lesions may include redness ( erythema ), macules , papules and vesicles . Secondary lesions could include alopecic plaques (with either increased or decreased pigment), excoriation , lichenification , secondary bacterial pyoderma, malassezia dermatitis, seborrhoea . Seasonality of signs would depend on allergen. Diagnosis is based on history and clinical signs, provocative exposure test, and patch testing with histopathology of positive reaction sites. Provocation test: Dog is bathed in hypoallergenic shampoo to remove all possible allergens from skin and coat. Dog placed in non allergenic environment for 14 days, then re-exposed to either normal environment or to suspect substances one at a time. Skin is observed for flare up of dermatosis for next 7-10 days. Treatment is ideally avoidance of allergen (or removal of allergen from environment). Where this is not possible systemic or topical glucocorticoids may be required.

Contact plate

Sterile nutrient plate used for culture of micro organisms e.g. bacteria.

Corticosteroids

Hormones or steroids which are naturally produced in the cortex of the adrenal gland and are resonsible for the control of glucose metabolism (glucocorticoids) and mineral and water homeostasis (mineralocorticoids). Mineralocorticoids (e.g. aldosterone) act via the kidney and are primarily responsible for maintaining water and electrolyte balances in the body. Glucocorticoids (e.g. cortisol) have a major role in glucose or carbohydrate metabolism, protein and fat metabolism, and have anti-inflammatory effects through prevention of phospholipid release and through several cell-based mechanisms. Corticosteroid is also commonly used to describe the group of synthetic medications which have varying degrees of either glucocorticoid or mineralocorticoid effects. Most commonly these medications are used for their anti-inflammatory and immunosuppressive effects. Examples of active ingredients include prednisolone, methylprednisolone, dexamethasone, or triamcinolone. The degree of glucocorticoid-like activity compared to mineralocorticoid-like activity varies between active ingredients. Synthetic corticosteroids which are used primarily for the mineralocorticoid effects include deoxycortone pivalate (DOCP) and fludrocortisone.

Crust

Either a primary lesion (e.g. with primary seborrhoea) or secondary skin lesion formed when exudate, serum, pus, blood, cells, scales or medications dry and adhere to the skin surface. Colour may be used to indicate source or depth of lesion, for example darker crusts may indicate deep tissue damage or haemorrhage.

Cryptococcosis

A fungal disease caused by infection with the yeast-like species Cryptococcus neoformans which may be found in the environment, particularly around pigeons. Immunosuppression may predispose to disease. The disease is rare in dogs, younger animals are more commonly affected with neurological or ocular signs observed. Skin lesions may occur and are seen mostly on the nose, lips and claws. Lesions may appear as papules , nodules , ulcers, abscesses or draining tracts. Diagnosis is based on cytology or biopsy with visualisation of the yeast-like organisms surrounded by a clear mucinous capsule. The disease is treated by administration of an appropriate antifungal medication.

Culture (for bacterial or fungal infections)

Growth of microbes on a nutrient culture medium (contact plate) for identification of bacterial or fungal species present. Sample is most commonly obtained from skin sites via cotton-tipped swab or scraping.

Cushing's disease

See hyperadrenocorticism.

Cutaneous adverse food reaction

Includes any reaction to food which manifests itself through skin lesions. This includes food hypersensitivity or allergy, toxic food reactions and food intolerance.

Cutaneous cytology

Microscopic examination of stained material such as tissue or fluid to assess cell type, cell appearance (neoplastic, necrotic, inflammatory), presence of bacteria or yeasts. A range of sampling techniques may be used depending on lesion location and type. Techniques include direct smears, impression smears, swab smears, skin scrapings and fine needle aspiration. Direct smear: Useful for fluid containing lesions. Method: A sharp object such as a needle tip or corner of a slide is used to collect a small amount of fluid from the lesion. The material is then smeared gently on the slide (minimising damage to cells). Fluid is allowed to dry on slide before staining. Impression Smear: Useful for moist or greasy lesions or those containing fluid. Areas sampled may include skin surface beneath crusts, fluid expressed directly from lesions, and pustules, papules, or vesicles where the roof of the fluid pocket has been gently removed. Method: A clean microscope slide is applied directly to the lesion site. As the sample is of greasy or fluid material, the slide should be allowed to dry (fluid) or heat-fixed (greasy or waxy samples) prior to staining. Swab Smear: Useful for dry crusty lesions, ear canals, interdigital sampling, or draining tracts or sinuses. Method: A sterile cotton-tipped applicator is moistened and inserted into the sample area (sinuses and canals) or rubbed rapidly over the skin surface (dry or interdigital lesions). Cotton tip is then rolled over the surface of a clean microscope slide. Waxy and dry samples are heat fixed and fluid samples are allowed to dry before staining. Skin Scraping : Useful for mite identification, sampling under crusts, vesicles or peeling skin (stratum corneum), or to collect cells from the surface of samples. Method: A surgical scalpal blade is scraped over the surface held at a 15-90 degree angle. Collected material is then wiped on the surface of a clean microscope slide and allowed to dry before staining. FNA: Useful for nodules, tumours, cysts, vesicles or bullae and pustules. Method: For fluid-filled lesions, a 20 - 22 gauge needle is attached to a 3 ml syringe and the sample is aspirated by gentle withdrawal of the syringe plunger. For solid lesions a 20 gauge needle and slightly larger 6 ml syringe are used and the plunger is withdrawn to the level of 3 - 4.5 ml.Suction pressure on syringe is eased and needle redirected to another part of the mass where the process is repeated. This is repeated 3-4 times. The suction is then released and the syringe is separated from the needle, filled with air, and reattached. The air is used to expell the contents of the needle on to a clean microscope slide. A second microscope slide is then used to gently smear the material across the surface of the slide. Fluid samples are allowed to dry and dry or greasy samples are heat fixed prior to staining.

Cutaneous Mucinosis

A condition in which excessive amounts of mucin, a jelly-like substance are found in the dermis of the skin. Condition is considered normal in Shar-Pei dogs where the high levels of mucin are responsible for the breed's characteristic skin folds.

Cuterebra

An opportunistic, parasitic infesation of the skin most commonly caused by the rodent or rabbit botfly Cuterebra spp. May rarely be caused by Hypoderma spp or Dermatobia spp. Dogs and cats are abnormal hosts. Flies lay eggs on vegetation or environment of the host. Animals are infected as they brush past the infested area. Eggs hatch in response to body heat from host and larvae enter the body through the mouth or nostrils during grooming or through open wounds. Larvae then migrate to subcutaneous tissue locations where they breathe through a tiny pore in the skin. After about 30 days the larvae exit the skin, fall to the ground and pupate. Emergence of adults from pupae may depend on environmental factors. Lesions in the skin are most commonly seen from summer to autumn and are seen as fistulous subcutaneous swellings about 1 cm diameter particularly around the head, neck and trunk. Hair over the lesion may be matted and cats in particular are likely to groom the area extensively. Secondary bacterial infections may occur resulting in purulent discharge from the lesion and often increasing pain associated with the lesions. Differential diagnosis is most commonly abscess or foreign body. Diagnosis is made by finding and identifying larvae. L3 (third instar) larvae are most commonly identified and are 5 - 10 mm in length , dark, thick and heavily spined. Less commonly identified L2 larvae are gray to cream in colour. DO NOT SQUEEZE SUSPECT LESIONS as rupture of the larvae may result in a chronic foreign body reaction and secondary infection. Treatment includes gentle removal of the whole larva by careful probing of the fistula with mosquito forceps. Area is flushed with saline, debrided if required and allowed to heal by granulation. Failure to heal may indicate a section of the larva remains in the wound or that reinfestation has occurred.

Cyclosporine

Cyclosporine (cyclosporin, cyclosporine A) is an immunomodulating drug which is primarily used systemically in dogs for treatment of atopic dermatitis and topically for management of keratoconjunctivitis sicca (dry eye). In the management of canine atopic dermatitis, cyclosporine is administered orally and concentrates in the skin where the mode of action results in both anti-inflammatory and anti-pruritic effects. Cyclosporine acts specifically and reversibly on T-lymphocytes, inhibiting the antigen-triggered release of chemical mediators by activated T-cells. It also inhibits mast cell degranulation, recruitment and activation of eosinophils, Langerhans' cell functions, and keratinocyte production of chemical mediators. In atopic dermatitis, cyclosporine effectively reduces pruritus and skin lesions. Cyclosporine is metabolised through the cytochrome p450 pathway (primarily in the liver), so the potential for drug interactions with inducers (e.g. phenobarbitone) or inhibitors (e.g. ketoconazole) of this pathway should be considered. Cyclosporine formulation may affect consistency of drug absorption. For further information see Atopica Cyclosporine, Novartis Animal Health) product label.

Dandruff

A condition where the skin is covered in dry bran-like scales. Also see Cheyletiella ("walking dandruff"), and seborrhoea.

Deer ticks

Ixodes scapularis, also called the black-legged tick. Preferred hosts are deer. I. scapularis may act as a vector for diseases such as Borrelia (Lyme disease), Anaplasma and Babesia .

Demodex

A parasitic mite which lives in the hair follicle of the host. The entire life cycle is spent on the host. The most common mite causing disease in dogs is Demodex canis. Two other Demodex species, a short and long tailed species, also rarely cause disease. Dogs normally carry small numbers of mites, however skin disease occurs when large numbers of mites are present.

Depigmentation

A loss of colouration (i.e. melanin) within the skin due to toxic or inflammatory damage to pigment creating cells (melanocytes).

Dermatophyte test media

A growth medium for fungal culture which turns reddish in colour as dermatophyte colonies (white in colour) are growing.

Dermatophytes

Fungi which are able to utilise skin keratin to survive in the superficial layers of the skin. Species commonly affecting dogs and cats include Microsporum and Trichophyton species.

Dermoid Sinus

A rare developmental condition resulting from incomplete separation of the neural tube from the skin. Lesions appear as one or more lumps on the dorsal midline. Sinus depth may range from a blind sac to connection with the dura mater of the spinal cord. Infections may result in neurological signs. Diagnosis is based on presentation. Treatment may involve surgical removal, depending on the depth of lesion. The condition is considered genetic and certain breeds are predisposed so affected animals should not be used for breeding.

Diascopy

A diagnostic test which is used to differentiate skin erythema caused by inflammation or vascular dilation versus erythema caused by bleeding in the skin. A clear piece of plastic or glass is placed over the erythematous lesion and pressure is applied. If the lesion blanches then the reddening of the skin is caused by dilation of blood vessels in the skin. No loss of colour indicates haemorrhage within the skin (petechia = small, echymosis = larger area).

Drug eruptions

An adverse drug reaction of the skin. The reaction may be immune-mediated (hypersensitivity), or non-immunologic. Any drug has the potential to cause a reaction. For some medications, the reactions are predictable (known to occur due to mode of action of the drug). Non-predictable or idiopathic reactions are thought to be associated with drug metabolism pathways within the individual, but the cause is often unknown. The type of hypersensitivity reaction/s involved may include types I, II, III, or IV. Due to the variety of possible reactions involved, drug reactions may present like almost any other skin disease. The most common lesions in dogs include urticaria / angioedema , erythema multiforme, contact dermatitis, exfoliative dermatitis, macular or papular lesions, and pruritus with subsequent self-trauma. Diagnosis is generally based on history (appropriate timing of onset in relation to drug administration, usually within 1-3 weeks), lack of alternative causes, and response to dechallenge. A knowledge of prior events associated with the medication may be helpful, but as hypersensitivities occur in only a small proportion of the population this information may not be available. Treatment involves drug withdrawal, symptomatic therapy, and avoidance of any similar medications in the future. Prognosis is often good, but this depends on severity of lesions and number of body systems involved.

Ear margin dermatosis

A keratinisation defect of dogs, particularly affecting breeds with pendulous ears (e.g. dachshund). Clinical Signs: seborrhoea of medial and lateral margins of the pinna characterised by greasy plugs (follicular casts) adhering to the skin and hairs.Lesion may start as a small focal area and spread to include entire ear margin. Severe or chronic cases may develop thick hard crusting on ear margins accompanied by scratching, head shaking or rubbing of the area (see risk factors for aural haematoma ). Painful cracks or fissures may appear in crust and surrounding tissue. Treatment: no known cure. Check diet of dog and minimise exposure to dry heat sources such as heaters, central heating ducts, wood fires etc. Manage by bathing with antiseborrhoeic shampoos. For hard crusted areas soak in warm water for 5 - 10 minutes before treating with shampoo. Shampoo every 24 - 48 hours followed by application of an emollient or moisturiser. As appearance of ears returns to normal (may take up to 2 weeks), shampooing is reduced to an 'as needed' basis. In some severe cases where cracks or fissures have appeared in the pinna, surgery may be required.

Ehlers-Danlos syndrome

Initially identified in humans, Ehlers-Danlos syndrome is a group of inherited connective tissue disorders caused by a defect in collagen synthesis. Collagen is a protein component of connective tissue which helps support the skin, muscles, ligaments and organs of the body. Severity of disease depends on the type of mutation varying from mild to life-threatening. Where skin is affected severe fragility and bruising may result. Skin texture may be soft and sagging. There is no known cure, treatment is supportive. A similar syndrome has been identified in Himalayan cats, some domestic cats and sporadically in dogs.

Electron beam therapy

A method of external beam radiation therapy. Electrons are accelerated via a machine toward the skin. Used mostly for lesions on or near the skin surface, particularly tumours.

Elimination diet

A diagnostic technique for identification of adverse food reactions such as food allergy dermatitis. Either a hydrolysed diet or a diet consisting of a protein and carbohydrate to which the dog has had no/minimal exposure (novel diet) is selected. Dog is trialled on this diet for a period of 8 - 10 weeks to assess improvement in clinical signs. No other flavoured treats or medications are administered. Food allergy is then confirmed by rechallenge with the original diet.

ELISA (Enzyme-linked immunosorbent assay)

A fast diagnostic technique used to detect the presence of proteins such as antibody or antigen in a test sample. The technique is based on formation of antigen-antibody complexes, and the ability to show the presence of these complexes by means of an enzyme marker (e.g. causing colour change). ELISA antigen detection kits are typically used to measure the presence of specific microbial (e.g. viral) or parasitic antigens. They identify whether the organism is present in the blood or tissue at the time of testing (e.g. heartworm antigen test). ELISA antibody detection kits measure whether the animal has had previous exposure ( and formed an antibody-based immune response) to a particular antigen. A test surface is created which contains fixed amounts of the particular antigen. When the test sample is added, any antibodies which target the particular antigen will bind to the antigen on the test surface. A solution containing enzyme-marked secondary antibodies is added. These enzyme-linked antibodies will only attach to the test surface if antibodies from the test sample have adhered to the test surface antigen. A substrate is added which changes colour on exposure to the marker enzyme. Colour change indicates a positive response (i.e. the test sample contains the relevant antigen/antibody. ELISA tests are available for many forms of infectious disease as well as for identification of potential allergens in allergic skin disease. Sensitivity and specificity of the test should be considered when interpreting results. Considerations include cross-reactivity, influence of prior vaccinations, and the animal's ability to form an antibody-based immune response (if measuring antibodies).

Elizabethan collars

Large plastic or material collars which extend forward from the neck to the tip of the nose creating a cone-like shield around the dog or cat's head. Used to prevent self-trauma such as licking of wounds, bandages or sutures, or to prevent removal of oxygen or feeding tubes in hospitalized patients.

Endocrine alopecia

Typically non-pruritic, non-inflammatory symmetrical hair loss due to alterations in hormone levels which affect the hair follicle cycle (follicular atrophy) or which affect the hair follicle structure (follicular dysplasia), causing hair to fall out. Unless sex-hormone related, endocrine alopecia is generally accompanied by other systemic signs. In this case common causes could include hypothyroidism or hyperadrenocorticism . Treatment is by identification and treatment of underlying cause.

Eosinophil

A granular leukocyte (white blood cell) with coarse round granules present in the cytoplasm. The cells are recognised on microscopy by their lobulated nucleus and the red colouration of the cytoplasmic granules after the addition of Eosin stain. Eosinophils are produced in the bone marrow and normally present at low levels in the circulation. They play a major role in hypersensitivity reactions, controlling tissue inflammation and defending against extracellular parasites. They may also act as phagocytic cells. The role of eosinophils is achieved through extensive interaction with surrounding cells (through positioning of receptors on the cell surface and secretion of chemical messengers) as well as production of toxins and enzymes with tissue activity. Circulating numbers are most commonly reduced due to high levels of circulating corticosteroids (either internal or drug-induced). Numbers may be seen to increase (eosinophilia) due to parasitic disease, IgE mediated hypersensitivity reactions, where inflammation is present in mast cell rich tissues, or due to cell neoplasia.

Epidermal collarette

A secondary skin lesion. A circular rim of epidermal scale seen either after a fluid filled swelling (e.g. a pustule, papule, vesicle or bulla) has ruptured or as a result of inflammation stimulating increased keratin production at the edge of a pustule or papule.

Epidermal hyperplasia

An increased thickness of the non-cornified epidermis due to an increased number of cells. A common feature of chronic inflammatory disease.

Epidermal oedema

An increase in fluid within the epidermis resulting in swelling of tissue. May be either intracellular (within the cell) or intercellular (between cells, ' spongiosis '). Commonly a feature of acute or sub acute inflammatory dermatoses.

Epidermis

The outermost layer of the skin. The epidermis is divided into five layers: stratum corneum (horny layer), stratum lucidum (clear layer), stratum granulosum (granular layer), stratum spinosum (spinous layer) and stratum basale (basal layer) which overlies the dermis. The majority of skin pigment (in melanocytes) is within the basal layer. This layer also is responsible for replication of major cells within the epidermis (keratinocytes). Junctional complexes link the basal layer to the dermis.

Epitheliotropic lymphoma

A malignant tumour of the skin and mucous membranes originating from T cells (or T lymphocytes). Also known as 'mycosis fungoides' or 'cutaneous lymphoma'. The disease tends to occur in middle-aged to older dogs and cats, the underlying cause is unknown but an association with Feline Leukaemia Virus (FeLV) infection in cats is suspected. A study has shown that the risk of developing epitheliotropic lymphoma is approximately 12 times higher in atopic dogs than in non-atopic dogs. Early lesions may resemble many inflammatory skin diseases with signs including erythema , scale , pruritus, depigmentation , alopecia, plaques , ulceration and crusting. Single or multiple skin nodules may also occur. Lesions may be generalised or may occur in a localised area and are often reported in the oral tissues and mucocutaneous junctions (such as around the eyes, nose and lips). Differential diagnoses include autoimmune skin diseases such as pemphigus vulgaris, bullous pemphigoid and lupus erythematosus . Treatment may include surgergy, radiation therapy, or chemotherapy. Prognosis is poor and treatment objectives centre on control of symptoms, slowing progression of the disease and improving quality of life.

Erosive and ulcerative diseases

An erosion is a shallow skin defect which has not penetrated the basal layer of the epidermis. Commonly, this may be caused by self trauma or epidermal disease and does not result in scarring. Ulcers penetrate to the level of the dermis and often scar on healing. Examples of ulcerative diseases in dogs include vasculitis , autoimmune disease and deep pyodermas .

Erythema

Reddening of the skin due to dilation of capillaries in the area. Erythema may occur with inflammation, infection or trauma. The redness can be differentiated from tissue haemorrhage by diascopy . Erythematous areas will blanch when pressure is applied.

Essential fatty acids (EFAs)

Polyunsaturated fatty acids which cannot be synthesised by the dog and must therefore be provided in the diet. There are two major groups of essential fatty acids, omega -3 and omega -6 fatty acids. In dogs, the two major essential fatty acids for skin function are linoleic acid (omega - 6) and linolenic acid (omega - 3). Fatty acids are important components of cell membranes, provide luster to the haircoat and (particularly linoleic acid) moderate water exchange on the skin surface allowing skin to stay smooth. The essential fatty acids may compete with arachidonic acid for metabolism within the inflammatory cascade (involving cyclooxygenase and lipoxygenase enzymes), potentially reducing the amount of inflammatory mediators in the tissue. This could be particularly important in hypersensitivity reactions. Dogs with dry seborrhoea have a deficiency of linoleic acid in the skin, oral supplementation can improve the clinical signs. Dietary deficiencies of essential fatty acids may result from insufficient oils in the diet, over cooking, or poor food storage.

Excessive shedding alopecia

An increased rate of hair shedding which is not accompanied by a similar rate of hair regrowth, creating areas of alopecia. May be seen, for example in endocrine disorders and follicular dysplasia.

Excoriation

A secondary lesion caused by biting, scratching or rubbing which results in erosion or ulceration of the skin (i.e. self trauma). Skin trauma may predispose to secondary infection. Excoriation is a common indicator of pruritus.

Exocytosis

Exocytosis has two potential meanings: 1) Infiltration of the epidermis by inflammatory cells or circulating blood cells. 2) A process by which a cell discharges large particles into the surrounding environment.

Exudate

Fluid which has escaped from blood vessels and entered tissues usually as a result of inflammation. Fluid is high in protein content and cellular debris. May or may not contain micro organisms (e.g. bacteria).

Fibroblast

Fibroblasts are the most ubiquitous cell type within the body. The are important structural components of tissue as well as having a role in immunoregulation within their specific tissue. Fibroblasts are able to secrete chemical mediators which recruit inflammatory and immune cells to the area and also regulate cell growth. The structure and function of fibroblasts will vary depending on their tissue location.

Fibroma

Uncommon benign neoplasm (tumour) of the skin originating from fibroblasts in the dermis or subcutis. Tumours are generally found in older female dogs, and often present as solitary well-circumscribed lesions. The tumours may appear pedunculated or more dome-shaped and some are highly pigmented. Diagnosis is by cytology and histopathology. Treatment ranges from monitoring to surgical excision.

Fibrosarcoma

An uncommon neoplasm (tumour) of the canine skin originating from fibroblasts in the dermis or subcutis. Firbrosarcomas are most frequently found in older, female dogs particularly on the trunk and legs. Lesions are often solitary but irregular and poorly circumscribed. Hair loss and ulceration may be seen. Diagnosis is by cytology and histopathology. Treatment involves wide surgical excision.

Fibrosis (dermal)

The laying down of fibrous tissue in the skin, usually following tissue granulation with oedema and inflammation. The end point of fibrosis can be scar formation (sclerosis).

Fine Needle Aspiration

See cutaneous cytology

Fissure

A secondary skin lesion. A linear crack or cleft either within the epidermis or extending through the epidermis into the dermis. Generally occurs where thick, inelastic skin becomes swollen due to inflammation or trauma.

Fistula

A tunnel-like passage within tissue which may connect different body tissues or cavities. For example: Perianal fistulae ; tube-like formations which occur in the in the skin and deeper tissues around the anus.

Flare factors

Stimuli which will cause a dog with pruritic skin disease to start showing clinical signs (e.g. itching, scratching, chewing, or rubbing). The point at which a dog will start to show clinical signs is called the "pruritus threshold". Below this, a level of inflammatory disease may be tolerated by the dog without any indication of discomfort. In allergic skin disease, the therapeutic aim is to keep animals below their pruritus threshold. Flare factors can include bacterial/yeast infections, parasites, nutrition, stress, other skin disease, temperature, humidity and other environmental factors. The presence of multiple flare factors will increase the possibility of dogs exceeding their pruritus threshold and displaying clinical signs. Reduction of flare factors can enhance the success of clinical treatments or minimise the need for medical therapy.

Flea

A small, laterally compressed blood-sucking parasitic insect, often host-specific. An obligate parasite (adult requires a blood meal in order to reproduce). Only the adult lives on the host, immature stages (egg, larvae, pupae) are found in the environment. There are over 2000 species of flea in the world. The most common flea species affecting cats and dogs is the cat flea (Ctenocephalides felis).

Flea Allergy Dermatitis

Flea allergy dermatitis (FAD) or Flea bite hypersensitivity is a very common pruritic, papular skin disease caused by hypersensitivity to flea salivary antigen.

Fly bite dermatitis

Inflammation of the skin resulting from trauma due to biting flies. Flies such as stable flies ( Stomoxys calcitrans ) generally attack the face or ears of dogs. Skin becomes reddened (erythema) and haemorrhagic crusts form where serum and blood ooze from the wound. Hypersensitivity to the insect bite may increase severity of lesions. Pruritus ranges from mild to severe. Treatment involves cleaning the environment to minimise areas in which flies may breed, topical antibiotic/anti-inflammatory ointments if required, and insect repellants applied daily to affected areas. As flies are generally found outdoors, dogs may be housed inside to aid recovery. Black flies ( Simuliidae spp) are smaller flies that tend to be found in spring - summer near shaded, running water. They generally attack areas with little or no hair. Lesions tend to be more severe with intense pruritus and development of ulcers, haemorrhage and severe self trauma in addition to crusting papules. Treatment for all fly bite dermatitis is similar; symptomatic, insect protection, and avoidance or environmental management.

Fold dermatitis

An inflammatory bacterial skin disease which occurs within the humid environment of a skin or lip fold. Examples include body fold dermatitis and skin fold dermatitis .

Follicle

A sac or pouch-like depression or cavity. A tubular invagination of the epidermis enclosing the hair roots and from which the hair grows.

Follicular cyst

The most common form of skin cyst in the dog. Any dog type can be affected. Cysts are usually solitary and located on the head, neck, trunk and proximal limbs. They appear within the dermis or subcutaneous tissue as well-circumscribed, round, smooth lesions. Discharge, if it occurs is thickened and yellow-brown to grey in colour. Uncommonly, multiple cysts may appear at pressure points or on the top of the head in young dogs. Treatment ranges from monitoring to surgical excision. Do not squeeze or express lesions manually (can result in dermal or subcutaneous tissue reactions).

Folliculitis

Inflammation of the hair follicle, generally due to infection ( bacterial folliculitis ). May be superficial or spread deeper into the follicle (see deep pyoderma ). If the follicle ruptures, the lesion is called furunculosis.

Food allergy

Food allergy (or canine food hypersensitivity) is an adverse food reaction caused by hypersensitivity to allergens within the diet. Cutaneous food allergy (or canine food hypersensitivity) is a non-seasonal pruritic disorder of dogs caused by a hypersensitivity reaction to one or more antigenic ingredients in the dogs diet. Cutaneous adverse food reaction may manifest as atopic dermatitis in some dogs, ie food may trigger flares of AD in hypersensitive dogs. Food allergy may also present as gastrointestinal signs such as vomiting, diarrhoea, flatulence or borborygmus.

Food Elimination Trials

See elimination diet.

Fungal skin diseases (mycoses)

A group of skin diseases caused by either yeasts or moulds. Not all fungi cause disease. Many yeasts and moulds may be found on the skin surface and in the haircoat of normal, healthy animals. Immunosuppression or skin trauma or disease may increase the likelihood of fungal infections occurring. As many yeasts and moulds may be found on normal skin, sample collection, culture and identification are important in achieving a diagnosis. Superficial mycoses are fungal infections involving the superficial layers of the skin, hair and claws. Examples include dermatophytosis (ringworm, tinea), candidiasis (yeast), and Malassezia (yeast). Topical antifungal therapy (creams or lotions, shampoos, rinses) may be sufficient in most superficial yeast infections and some dermatophyte infections. For dermatophytosis topical therapy may be used in conjunction with systemic treatments. Subcutaneous mycoses ('intermediate mycoses') are fungal infections which have gained access to the deeper layers of the skin, usually through trauma or immunosuppression. Systemic mycoses ('deep mycoses') are fungal infections of internal organs which may spread to the skin via the bloodstream. Sytemic antifungal therapy is required for these conditions.

Furunculosis

A lesion occurring in deep pyoderma where rupture of an infected hair follicle leads to release of micro organisms and cellular debris into the surrounding dermis.

Granulomatosis

The formation of multiple granulomas e.g. lymphomatoid granulomatosis.

Haemangioma

An uncommon benign neoplasm (tumour) of canine skin originating from the endothelial cells of blood vessels in the dermis and subcutis. Sun damage may be a contributing factor. Tumours are generally found in older dogs, particularly on the abdomen of light-coloured animals with thin coats. Lesions tend to be well circumscribed and blood-coloured (blue-red-black). Diagnosis is by histopathology. Treatment ranges from monitoring to surgical excision.

Haemangiosarcoma

An uncommon malignant neoplasm (tumour) of canine skin originating from the endothelial cells of blood vessels in the dermis and subcutis. Sun damage may be a contributing factor. Tumours are generally found in older dogs, particularly on the trunk and extremeties. Lesions are often rapidly growing and hair loss, haemorrhage, ulceration and skin thickening are common. Where sun is a contributing factor multiple variably circumscribed, red-blue lesions may be observed in the dermis. Subcutaneous haemangiosarcomas are larger, poorly circumscribed, red-blue spongy masses. Diagnosis is through histopathology. Treatment involves wide surgical excision. Local recurrence and metastases are common.

Hair plucking

See trichogram

Histiocytoma

One of the most common canine skin neoplasms, generally considered benign. Tumours are most frequently seen in young dogs, usually as a single lesion on the head, legs, or pinnae (ear). They usually appear as small, firm, well-circumscribed dermal lesions which may ulcerate. Rapid growth is common. Diagnosis is by cytology or histopathology (biopsy). Treatment ranges from monitoring to surgical removal. Spontaneous resolution may occur.

Hives

See urticaria.

Hookworm

A nematode parasite of the small intestine (i.e. intestinal worm). The adult hookworm female sheds eggs in the host faeces. Eggs develop in the ground to the infective larval stage (L1). Infective larval stage may enter host by ingestion (if licked off ground, paw, or object), burrowing through skin, by infecting an abnormal host which acts as prey for dogs and cats (such as birds or rodents). In some species of hookworm (e.g. Ancylostoma caninum ) the larvae may infect puppies through the mother's milk. Cutaneous or skin migration generally occurs in parts of the body which have contact with the contaminated ground. Migration through the paws can result in inflammation, thickened pads, pododermatitis , or nail growth abnormalities. In other areas of skin, inflamed tracks may be seen in the skin where the parasite has entered. Larvae migrate through body tissues and reach the intestine where they mature and attach to the lining of the intestinal wall. The parasite may reach adulthood within a host within 2-3 weeks of original infection. Infected dogs or cats may show signs of diarrhoea, haemorrhagic diarrhoea, weight loss and anaemia. While not a normal host, people may also potentially be infected if their skin rests on contaminated ground (zoonotic disease). The most common hookworm species in the dog around the world is Ancylostoma caninum. Other species include A. braziliense (tropical climates) and Uncinaria stenocephala (temperate or cooler climates). Treatment of skin lesions is generally symptomatic. As the source of infection is the environment, dogs are treated with an intestinal anthelmintic. Careful environmental management through regular collection and disposal of animal faeces is important in minimising the risk of infection to animals or to people. Risk to people may also be reduced by measures such as covering sandpits when not in use by children, and ensuring all family members wash their hands before handling food.

Hormonal therapy

Hormonal therapy may be used to describe a range of treatments, usually involving the administration of synthetic hormones to achieve a particular therapeutic effect. The most common hormone therapy in treatment of pruritic skin disease is the administration of glucocorticoids (corticosteroids) for their anti-inflammatory and immunosuppressive effects. Hormone therapy may also be considered where skin disease is resulting from an underlying endocrinopathy such as hypoadrenocorticism, diabetes mellitus, or hypothyroidism . Melatonin, a hormone naturally secreted by the pineal gland has been considered for the treatment of non-endocrine alopecia. Melatonin has a natural role in regulating hair growth and pigment. Hormone therapy has also been considered in management of psychogenic skin disorders.

Hot spot

Superficial bacterial pyoderma, also called pyotraumatic dermatitis.

Hydropic degeneration

Intracellular oedema of the basal layer cells of the epidermis. Hydropic degeneration is uncommon, often localised and most commonly associated with autoimmune diseases such as lupus erythematosus, erythema multiforme, cutaneous drug eruptions, toxic cell damage or vasculopathies.

Hygroma

The formation of a bursa in the subcutaneous tissue overlying a bony prominence (e.g. the elbow). The bursa forms as a result of chronic trauma and tissue necrosis over a pressure point. Initially fluid-filled, the lession may become an abscess or granuloma. Treatment in the early stages may include bandaging and modifications to the dog's environment. More chronic lesions may require surgical drainage or repair.

Hyperadrenocorticism

Also called Cushing's syndrome. A common endocrine disease of dogs resulting from excessive levels of cortisol in the body. Elevated cortisol levels are caused by increased production from the adrenal cortex. Increased production may occur as a result of disease in the pituitary gland in the brain (responsible for modulation of secretion from the adrenal gland), or a tumour of the adrenal gland. Iatrogenic hyperadrenocorticism may also occur in dogs treated with excessive levels of glucocorticoids (corticosteroids). As cortisol affects many body systems, the most common presenting signs are generally increased drinking, urination and appetite. Potential skin changes include symmetrical alopecia, thinning of the skin, and calcinosis cutis. Additional signs may include a pendulous appearance to the abdomen and muscle wastage. Diagnosis is generally based on clinical signs and adrenal function tests . Treatment of iatrogenic hyperadrenocorticism includes gradual weaning from medication. Treatment of pituitary or adrenal hyperadrenocorticism varies depending on the lesion location. Chemotherapy is generally considered for adrenal gland tumours.

Hyperhidrosis

Excessive sweating.

Hyperkeratosis

A histopathology term for increased thickness of the stratum corneum (outermost layer of the epithelium). The stratum corneum may appear thicker due to an increase in actual thickness, or because the underlying epidermis has become thinner (rare). Usually reported in conjunction with thickening of the epidermis (hyperplasia). Nucleation of cells (orthokeratotic) or lack of nucleation (parakeratotic) may provide an indication of underlying pathology.

Hyperpigmentation

An increase in colouration within the skin due to increased deposits of melanin within the epidermis. Pigment change may be localised or diffuse and may occur within the basal layer or throughout the epidermis . Commonly seen in chronic inflammatory and hormonal dermatoses and occasionally in neoplastic or developmental disorders. Also called 'hypermelanosis'.

Hypersensitivity

Hypersensitivity reactions are exaggerated immune reactions to specific allergens. They have been roughly divided into 6 groups based on reaction type, timing, and cell types involved. Allergic or immune-mediated diseases may involve more than one of these hypersensitivity 'types'. Type I : Immediate or anaphylactic hypersensitivity Classically involves a genetic predisposition, exposure to allergen, specific IgE production and mast cell degranulation. Onset is within minutes and duration often no longer than 1 hour. Examples include anaphylaxis, urticaria , drug eruptions , food hypersensitivity , atopy , FAD , and angioedema . Type II : Cytotoxic hypersensitivity Involves antibody (IgE or IgG) binding to specific antigens on body tissues and resulting in cell destruction. Examples include blood transfusion reactions, pemphigus and some drug eruptions. Type III : Immune complex hypersensitivity Antigen-antibody immune complexes attach to blood vessel walls and activate complement (an immunological biochemical cascade), attracting neutrophils which release tissue-damaging enzymes. Examples include some drug eruptions , bacterial hypersensitivity and systemic lupus erythematosus Type IV : Delayed or cell-mediated hypersensitivity Classically involves antigen presenting cells (such as Langerhans cells in the skin) which process the antigen before presenting it to, and sensitising, T-cells. On further antigen exposure, the sensitised T-cells release chemical mediators, resulting in tissue damage. The reaction may not be apparrent for 24 - 72 hours. Examples include contact hypersensitivity , FAD , possibly Malasezzia sensitivity and some drug eruptions . Late phase reactions Neutrophils and eosinophils infiltrate the tissue initially, followed by monocytes. Reactions are mast-cell mediated and may occur 4 - 8 hours after exposure. Examples include FAD and atopy . Cutaneous basophil hypersensitivity . Mediated by T-cells or by specific antibodies (IgE or IgG). Tissues are infiltrated by basophils and large deposits of fibrin occur. Reaction is thought to occur about 12 hours after exposure and peak after 24 - 72 hours. Possibly important in ectoparasite reactions or hypersensitivities (e.g. fleas or ticks). Allergic or immune mediated disease may involve more than one of these hypersensitivity 'types'.

Hypopigmentation

A decrease in colouration within the skin due to toxic or inflammatory damage to pigment creating cells (melanocytes).

Hypothyroidism

A condition resulting from underproduction of thryoxine from the thyroid gland. Hypothyroidism may occur as a primary disease (due to disease within the thyroid gland, often immune-mediated) or as a secondary condition (due to disease in the pituitary gland or elsewhere in the body). The condition generally occurs in adult dogs. Clinical signs can include alopecia, weight gain, lethargy, depression, or neurological deficits. Immunosuppression resulting from hypothyroidism may result in secondary infections or diseases such as generalised demodicosis.

Hypotrichosis

The presence of less than normal amounts of hair.

Iatrogenic

Resulting from clinical treatment (such as drug therapy or surgery). An example is iatrogenic hyperadrenocorticism which may be induced by administration of corticosteroids.

Idiopathic

Occuring without a known cause.

IgE

A type of antibody (or immunoglobulin) which has an important role in hypersensitivity (or allergic) reactions and potentially in parasite reactions. Immunoglobulins are produced by B-cells and plasma cells. The presence of allergen specific IgE is measured in serology tests for allergic dermatitis (e.g. RAST and ELISA).

IgE mediated allergy

Classically includes type I and type II hypersensitivity reactions. See hypersensitivity.

Impetigo

A form of non-contagious superficial pyoderma (bacterial disease) affecting young dogs before or during puberty. Characteristic lesions are non-follicular subcorneal pustules in lightly haired areas of skin, particularly the ventral abdomen and axillary regions. Generally non-pruritic (pruritus may indicate infection of the hair follicle - see folliculitis ). Lesions may occur spontaneously or secondary to parasites, viral infection, poor nutrition or dirty environment. Large pustules, greater than 0.5cm diameter, (bullous impetigo) may indicate underlying endocrine disease. Infection generally involves coagulase positive Staphylococcus spp. but other bacteria such as Pseudomonas and E.coli may be present particularly in bullous impetigo. Treatment: Lesions may resolve spontaneously. Topical antibiotic or antibacterial creams may be useful for small numbers of lesions. For more widely distributed lesions, washing area with mild antibacterial shampoo every 24 - 48 hours until lesions resolve may be more practical. Considerations: Abnormal presentations (mature age or abnormal location such as facial lesions) warrants more careful investigation for underlying disease. Systemic antibiotics rarely required.

Inflammation

A localised protective tissue response induced by tissue damage. Classical signs include heat, redness, swelling and pain. Chemical mediators are synthesised from phospholipids which have been released from damaged cells. These chemical mediators (such as prostaglandins) can alter blood flow to the area, increase capillary permeability, and attract increased levels of white blood cells to the affected tissue. The overall effects include toxin dilution, isolation of affected tissue or causative organisms, and increased presence of defensive white blood cells.

Interdigital pyoderma

Bacterial infection of the skin of the foot. See pododermatitis and pyoderma.

Interface dermatitis

Skin disease characterised by histopathological changes involving the junction between the dermis and epidermis. Changes typically include either hydropic degeneration or lichenoid infiltrate. Hydropic degeneration is increased water absorption of cells generally associated with ischaemia, toxic injury or autolysis. Examples of diseases in which this may be observed in the dermo-epidermal junction include cutaneous adverse drug reactions , lupus erythematosus , vasculopathies and erythema multiforme. Lichenoid (lichen-like) infiltrate describes a banded infiltrate occuring parallel to the epidermis. Examples of diseases in which this may be observed include lupus erythematosus , erythema multiforme, pemphigus and adverse drug reactions. Cell bands often include lymphocytes and plasma cells.

Intradermal testing

A diagnostic test used for identification of allergens in allergic skin disease is measured as compared to negative (saline) and positive (histamine) controls. Hair is clipped prior to testing. A sample of allergen is injected into the skin and the resulting inflammatory reaction is measured (as compared to saline and histamine controls). Several allergens are often tested at once. Intradermal testing may be used as the basis for avoidance therapy or immunotherapy.

Juvenile pyoderma

See canine juvenile cellulitis.

Keratin

A fibrous protein which is the primary component in skin, hair, nails and horny tissues. The protein is made by keratinocytes.

Laser therapy

The use of a concentrated beam of light of a single wavelength for either surgery or lesion ablation. In canine skin, laser therapy may be used for removal or treatment of tumours, to achieve either surgical removal (e.g. of a tumour or nail) or rapid treatment of skin lesions particularly where multiple lesions exist. Benefits reported include reduced pain and bleeding, less destruction of surrounding tissues and sterilisation of the surgical field.

Leishmaniasis

Leishmaniasis is a serious multi-systemic disease caused by the Leishmania species of protozoa. The protozoa complete their life cycle between 2 hosts; sandflies and vertebrate hosts (such as cats, dogs and people). In dogs, the parasite infects the lymphatic cells. Skin damage is usually the result of immune-complex deposition and granulomatous inflammation. Incubation periods vary from weeks to years. Leishmaniasis can affect multiple body systems including the ocular, musculoskeletal, renal, haematologic, lymphatic, and gastrointestinal systems as well as the skin. Skin lesions vary and may include fine scale, hyperkeratosis , ulcerations or erosions, hypotrichosis, and alopecia particularly around the head, ears, pressure points and extremeties. Diagnosis is by serology and visualisation of the parasite in tissue samples. Leishmaniasis in dogs is extremely difficult to treat and relapses may occur.

Leokotriene inhibitors

Leukotrienes are potent chemical mediators of inflammation. Leukotriene inhibitors are medications which block the synthesis of leukotrienes or act as antagonists at the leukotriene receptor sites. Leukotriene inhibitors are used primarily in human asthma.

Lice

Lice are highly host specific insect parasites of the skin which complete their entire 3- 6 week life cycle on the host. There are both chewing and biting species of lice. Diagnosis is by demonstration of the parasites or their eggs ("nits") in the coat. Treatment is with an appropriate insecticide. As lice are often found on debilitated animals, consideration should be given to any underlying cause or disease.

Lichenification

A secondary skin lesion. Lines and markings in skin appear exaggerated due to thickening and hardening of skin. Often skin has increased pigment ( hyperpigmentation ).

Lidocaine

A form of local anaesthetic, also called lignocaine.

Lime Sulphur Solutions

Sulfurated lime, used as a topical rinse. Solution has degreasing, antifungal, antibacterial and parasiticidal properties.

Lip fold dermatitis

A form of intertrigo, a surface bacterial skin infection caused by rubbing or friction between lip folds. Increased humidity between skin folds in addition to the frictional trauma potentially predisposes to bacterial infection in fold dermatitis.

Lipoma

One of the most common benign neoplasms (tumours) of canine skin originating from subcutaneous fat cells (lipocytes). Tumours are often found in older dogs particularly on the thorax and may be single or multiple, well circumscribed, soft lesions in the subcutaneous tissue. Diagnosis is through histopathology. Treatment ranges from monitoring to surgical removal depending on lesion size and impact on quality of life.

Lupus erythematosus

A group of uncommon autoimmune diseases which may either be localised in the skin or may involve multiple body systems. The cause is unknown and thought to be multifactorial. There does appear to be a genetic predisposition. The reaction seen is (by classical definition) a type III hypersensitivity i.e. characterised by the deposition of immune complexes. Antibodies are also created against body tissues. Lupus erythematosus may possibly be triggered, for example, by viral infection, drugs, or other hypersensitivity reactions. Often the cause is unknown. The two most common forms described are systemic lupus erythematosus (a severe multisystemic disease) and cutaneous (or discoid) lupus erythematosus which is a relatively benign condition aggravated by sun exposure. Systemic lupus erythematosus may present as a multisystemic disease. Most commonly dogs have polyarthritis, proteinuria, fever and skin disease. Dogs may also have muscle wasting, lower than normal levels of red or white blood cells, enlarged spleen or lymph nodes, and oral ulcers. Less commonly signs of disease of the heart, lungs, neurological system or clotting disorders may be seen. Skin lesions range from vesiculobullous lesions or ulcers of the skin or mucocutaneous junctions, seborrhoea , alopecia, thickened or ulcerated footpads, panniculitis , to poorly responsive bacterial pyoderma . Lesions are most common in thinly haired areas (e.g. head, limbs, groin etc). Diagnosis is challenging and is based primarily on history and clinical signs, haematology and biochemistry results +/- biopsy, and serology for antinuclear antibody. Treatment involves resolution of secondary infections and administration of appropriate immunosuppressive therapies. Prognosis varies depending on how early the disease is diagnosed and which body systems are affected. Discoid lupus presents most commonly as depigmentation, scaling and erythema to the nose with loss of skin structure (smoothing from cobblestone appearance). Rarely lesions may be seen around the eyes, ears, genitals and limbs. Sun exposure exacerbates the lesions. Diagnosis is based on history, clinical signs and biopsy results. Treatment involves sun protection and administration of appropriate immunosuppressive medications. Prognosis is often good.

Lymphadenopathy

Enlargement of the lymph nodes. Lymphadenopathy may be either localised (in proximity to site of infection or disease) or generalised indicating systemic disease. Enlargement may indicate reactive lymph nodes (active immune response) or lesions within the lymphatic system (e.g. neoplasia).

Lymphocyte mediated allergy

Refer to type IV hypersensitivity.

Lymphocytes

White blood cells which are involved in both cell-mediated and antibody-mediated (humoral) immune responses. Lymphocytes are divided into three main types: B-cells (bursa or bone marrow derived) have receptors which are structured to recognise specific antigens. On contact with the antigen, B-cells develop into plasma cells and produce antigen-specific immunoglobulins (antibodies). T-cells (thymus dependant) are important in directing and modifying the immune response. T-helper cells interact with B-cells to stimulate the production of specific forms of antibodies. Suppressor T cells inhibit the production of antibodies. Additional roles of T-cells include direct destruction of target cells, modifying the activity of phagocytic cells (e.g. macrophages), inducing or suppressing delayed hypersensitivity reactions, inducing tissue rejection (e.g. grafts). Much of the direction occurs via chemical mediators produced by the T-cell (e.g. cytokines). These mediators may also affect vascular permeability, collagen production and coagulation. Natural killer cells carry receptors which recognise markers on the body's own cells and inhibit destruction of these cells.

Maceration

The softening of tissue through soaking.

Mackenzie brush technique

A method of collecting hair samples for fungal culture. A sterile toothbrush is gently brushed through the coat, collecting hair and cellular debris. Toothbrush is then placed gently onto surface of culture medium. May be used for detecting asymptomatic dermatophyte carriers (e.g. Microsporum canis).

Macrophages

Mononuclear white blood cells. Macrophages evolve within body tissues from monocytes produced in the bone marrow. Different macrophage types, and therefore functions, are present within different body tissues. Generally macrophages are involved in all phases of the immune response as phagocytic cells. Key roles include defence against intracellular parasitic micro-organisms and tumour cells. They can act as antigen presenter cells (for T-cells) and produce chemical mediators which affect tissue structure, and cellular immune responses. Tissue macrophages also have an important role in wound healing, attracting additional macrophages to the area, and moderating cell proliferation. Fusion of macrophages can result in the creation of multinucleated giant cells , which may function like macrophages in host defence against infection and are involved in the removal of large foreign objects.

Macule

A well circumscribed but non-palpable area of colour change within the skin (less than 1cm diameter). If the lesion is greater than 1cm diameter it is called a 'patch'. Colour change may result from hyperpigmentation, hypopigmentation, haemorrhage into the skin (purpura), or erythema. Names for macular lesions resulting from haemorrhage in the skin include petechiae (pin-point lesions less than 1cm diameter) and ecchymoses (larger than 1cm diameter).

Malassezia pachydermatis

A fungal yeast species most commonly responsible for dermatitis in the dog. Some dogs may have a hypersensitivity to Malassezia , therefore the presence of even small numbers of yeast could be significant and causing pruritus.

Mast cell tumour

One of the most common and potentially malignant canine skin neoplasms (tumours) which arises from mast cells in the dermis or subcutaneous tissue. Mast cell tumours may occur in dogs of any age. The lesions are usually solitary but may be multicentric. Their presentation ranges from variably circumscribed papules, nodules, or pedunculated masses through to cellulitis-like lesions. Colour may be skin-tone, hyperpigmented or erythematous. Palpation sometimes causes inflammation and oedema as vasoactive chemicals are released from the tumour. Diagnostic cytology may be indicative. Diagnosis is confirmed on histopathology where lesions are often graded to give an indication of prognosis. Treatments include wide surgical excision, chemotherapy and/or radiotherapy depending on malignancy. Metastases occur in approximately one third of dogs.

Mast cells

Mast cells, which originate from the bone marrow but develop and mature within localised tissues, have many roles within the immune and inflammatory responses. They can bind and destroy or consume (phagocytose) certain bacteria, release biologically active chemicals into surrounding tissue (e.g. histamines, cytokines and leukotrienes) and trigger the activity of B and T lymphocytes (e.g. antigen presentation).

Megestrol acetate

A synthetic progestin (hormone). Use in skin disease is likely to be extra-label.

Melanoma

A malignant tumour of melanocytes, the cells responsible for pigment production. Lesions are usually solitary and tend to occur on the head, lips, limbs, digits, scrotum, and trunk in dogs. In cats the head, lips and neck are frequently affected. Lesions are often ulcerated but otherwise vary in size, shape and colour (grey, brown, or black). Tumour may grow up to 5cm diameter in cats and up to 10cm diameter in dogs. On palpation lesion may be poorly or well circumscribed. Treatment is radical surgical excision but recurrence and metastases are common.

Melanophage

A macrophage or histiocyte which has phagocytosed large amounts of melanin.

Melatonin

A hormone secreted by the pineal gland during the hours of darkness. Melatonin is involved in regulating hair growth (e.g. changes in seasonal haircoat) and pigment.

Mites

Parasites of the acarine family. Skin disease in dogs may result from infestation with parasitic mites or exposure to environmental mites (hypersensitivity reactions). Common parasitic mites in dogs include Demodex , Sarcoptes , Cheyletiella , Otodectes and trombiculids . Environmental mites commonly implicated in atopic skin disease include the house dust mites ( Dermatophagoides spp) and storage mites ( Tyroglyphidae spp).

Mononuclear cells

A general name used to describe the group of white blood cells which have a non-lobulated nucleus. These include lymphocytes , plasma cells , monocytes and macrophages , and mast cells . (Note white blood cells with lobulated nuclei are called granulocytes.)

Mosquito bite hypersensitivity

Mosquito bites may result in the formation of a pruritic papule on the skin where an animal was bitten. Some animals may develop a hypersensitivity to the saliva introduced into the skin by a mosquito prior to feeding. Lesions initially appear as reddened (erythema) plaques that may appear eroded, ulcerated, necrotic or crusted. With chronic exposure nodules may develop with change in pigment (most commonly loss of pigment), hair loss (alopecia) and scaling. Lesions have also been reported on other thinly-haired areas such as foot pads, lips and chin. Differential diagnoses include dermatophyte infection or other immune mediated conditions such as atopic dermatitis , food hypersensitivity and pemphigus foliaceus. Diagnosis is based on history, lesions, and response to an avoidance trial (hospitalisation or indoor housing for 5 days). Improvement when mosquito repellants are applied may also be indicative. Alternatively rule out differential diagnoses by biopsy (may not rule out hypersensitivities). Treatment and management involves avoidance (housing away from mosquitos or use of repellants) ideally or administration of glucocorticoid medication.

Multinucleated giant cells

A fusion of macrophages which may function like macrophages in host defence against infection and are involved in the removal of large foreign objects.

Mycobacteria

A species of intracellular bacteria. The pathogenicity of this species varies. The mycobacteria responsible for tuberculosis and leprosy are obligate pathogens, unable to reproduce outside the host. Most mycobacterial species are normally found in the environment but may occasionally cause disease. Tuberculous lesions are rare in dogs and may be caused by either the human species ( M. tuberculosis ) or cattle species ( M. bovis ). Lesions are more common in internal organs but may rarely be seen as one or more cutaneous ulcers, abscesses, plaques or nodules. The lesions may involve subcutaneous tissues as well as the skin and may discharge a thick, purulent, malodorous and yellow-green material. Commonly affected areas include head, neck and limbs. Signs of systemic disease and lymph node enlargement are often present. Diagnosis is on presentation, radiography, biopsy with histopathology or culture. Human test kits have also been used in dogs. Due to the high risk of transmission to humans, euthanasia is frequently recommended. Canine leprosy (nodular lesions which may ulcerate) seems to most commonly affect short-coated dogs on the head and ears. Diagnosis is based on presentation and confirmed if acid-fast bacilli are seen on direct smears or biopsy. Treatment is surgical excision. Opportunistic infections may be difficult to manage, surgical excision may be curative for small lesions. An appropriate antibiotic should be selected for larger lesions based on culture results as drug susceptibility varies. Treatment duration is often prolonged.

Mycoses

See Fungal skin diseases.

Nasal depigmentation

Also called nasal hypopigmentation. A syndrome which has been reported in several dog breeds including Labrador retrievers, Golden retrievers, Poodles, Pointers, Doberman pinschers, and white German shepherds. Dogs are born with a black nasal planum and the colour fades to brown or whitish over time due to loss of pigment in the nasal planum. Generally associated with ulcerative diseases or those affecting the basal cell layer of the epidermis. Reduction in pigment in some breeds may be seasonal. Note loss of pigment in the nasal planum may also be observed in ulcerative or erosive diseases or those characterised by damage to the basal cell layer.

Necrosis

Cell death as indicated by changes in structure due to enzymatic breakdown.

Neoplasia

The formation of a tumour, a new and abnormal growth where cell multiplication has become uncontrolled and progressive.

Neutrophils

A granular leukocyte (white blood cell) or "granulocyte" which originates from the bone marrow. Granulocyte is used to describe the white blood cells with multilobulated nuclei. Neutrophils are normally the most common white blood cell in circulation. The cells are rapidly drawn to a site of infection and are responsible for defence against most invading micro-organisms. Neutrophils are phagocytic cells, ingesting the target micro-organisms and destroying them as the neutrophil dies. Reduced amounts of neutrophils in the blood is called neutropenia. Numbers may be reduced due to infection or due to reduced production. Neutropenia due to infection is usually followed over time by an increase in immature neutrophils (band cells) in the blood stream . This is called a "left shift". Increased numbers of neutrophils is called neutrophilia.

Nikolsky's sign

A diagnostic test which may indicate the presence of diseases characterized by loss of cell cohesion within the skin (such as pemphigus complex, toxic epidermal necrolysis or erythema multiforme major). Gentle pressure is applied to the edge of an ulcer or erosion, the surface of a vesicle or to the skin surface. If the outer layer of skin is easily rubbed off this indicates possible loss of cell cohesion.

Nocardiasis

A rare bacterial skin disease caused by Nocardia spp which are common gram positive bacteria in the soil. Wound contamination, inhalation or ingestion especially in immunocompromised animals may lead to the formation of pyogranulomatous and suppurative lesions in the skin or lungs. Signs of infection include cellulitis , ulcerated nodules and draining abscesses. Lymph nodes are often enlarged. Lesions often occur in areas which have been wounded, particularly those in contact with soil (e.g. limbs and feet). Cats may develop panniculitis-like lesions on the ventral abdomen. If infection develops in the chest (pyothorax), animal may also be systemically unwell. Main differential diagnosis is actinomycosis (or mycobacteriosis for panniculitis-like lesions in cats). Diagnosis is by direct smear of fine needle aspirates, culture and biopsy. Specialised stains for acid-fast organisms is required (Gram's or Brown-Brenn stains). Nocardia spp are gram positive aerobes, partially acid-fast and have a branching filamentous appearance. Actinomyces spp are not acid-fast. Treatment includes antibiotics (continued for at least 1 month after remission), and surgical drainage. Antibiotic sensitivity testing is recommended. Prognosis is guarded.

Nodular skin diseases

Diseases characterised by the formation of discrete cell clusters within the skin. Nodules may be described as papular lesions which have expanded in height, width and depth. Potential nodular diseases include parasitic, pyodermas , mycoses , dermatophytoses , neoplasia, cysts, lupus , juvenile cellulitis, sebaceous adenitis or mycobacterial infections .

Nodule

A solid well circumscribed raised skin lesion of greater than 1cm diameter. Often extends into deeper skin layers. Nodules are a primary skin lesion.

Otic Swabs

Collecting a sample from the ear canal on a sterile cotton-tipped applicator for cytology or culture and sensitivity diagnostic testing. Also called ear swab.

Otitis Externa vs. Media

Inflammation of the ear. Otitis externa is inflammation of the ear canal. Signs may range from reddening (erythema) of the skin of the ear canal, through to pruritus and head shaking, scaling, inflammation (narrowing the canal), discharge (due to increased waxy or purulent secretions), bad odour, scratching or pawing at the ear, pain on palpation of the auricular cartilage and rotation of the head with affected ear nearest the ground. Potential causes include parasites (e.g. ear mites ), primary skin disease, foreign body (e.g.grass seeds), neoplasia, or infection. Otitis media : Inflammation of the middle ear. May cause facial nerve paralysis (e.g. facial palsy, Horner's syndrome). Inflammation or infection spreading to the temperomandibular joint (the hinge of the jaw) may cause pain to animals when eating.

Otodectes cynotis

The ear mite. A surface living mite which inhabits the external ear canal and surrounding skin in dogs and cats. Life cycle is completed in 18 - 28 days. Larvae emerge from egg and moult through 2 nymphal stages before becoming adults. Clinical signs include shaking of the head, scratching at the ears, inflammation fo the ear canals and cerumen, serous or purulent exudates developing. Secondary infection may occur. In severe infestations lesions may spread to other body parts. Mites are transmitted from animal to animal through close contact. Diagnosis is by observation of mites in ear canal on otoscopic examination or on ear swab. Treatment includes treatment of secondary bacterial or fungal infections and application of an appropriate acaricide via ear drops or systemic treatment. Cleaning of the ear canal is recommended. All dogs and cats in house of infected animal must be treated. Mite infestation of people (zoonosis) is rare.

Panniculitis

Inflammation of subcutaneous fat cells.

Papilloma

A neoplasm of the epithelium often caused by the canine papillomavirus. One of the most common canine skin neoplasms. The virus is transmitted by direct contact or via fomites. Incubation period is 1 - 2 months. Latent infections may become active if animals are immunosuppressed. Also called "warts" and "verrucae". Presentations in dogs include cutaneous inverted papillomas (younger dogs, ventrum and inguinal region mostly), oral papillomatosis (frequently younger dogs), cutaneous papillomas (often older dogs) and multiple pigmented papules or plaques . Squamous type papillomas are more common than fibrous papillomas. Diagnosis is confirmed on histopathology. Lesions may resolve spontaneously or surgery may be required. Virus may be associated with the development of squamous cell carcinomas

Papule

A primary lesion. A small, solid raised area of skin up to 1cm in diameter.

Pasteurella

A rod-shaped, gram negative species of bacteria which is a facultative anaerobe.

Patch testing

A diagnostic test occasionally used in allergic skin disease for identification of substances to which a dog has become hypersensitised (allergic). Hair is clipped prior to testing. A sample of the suspected substance (allergen) is placed on the surface of the skin and held in place for a period of 48 hours. Skin is observed immediately after patch removal and for up to 5 days afterwards to assess the presence of any inflammatory reaction. Skin biopsies may be taken. A key challenge in using patch testing is keeping the patch on one area of skin for 48 hours. Dogs may attempt to remove the patch, particularly if the area is pruritic. Additionally, localised irritation (rather than hypersensitivity) should be ruled out for any positive reactions. Test is used most commonly for diagnosis of contact allergies but may be considered for atopic dermatitis . Alternative diagnostic techniques include avoidance/provocation (contact allergy), serology ( RAST or ELISA testing), and intradermal testing.

Pediculosis

Infestation with lice.

Pemphigus

Pemphigus complex is a group of uncommon autoimmune diseases of the skin and mucous membranes resulting from a type II hypersensitivity. Lesions include vesicles , bullae, and pustules and are characterised by loss of cohesion between keratinocytes (acantholysis). Pemphigus vulgaris results in vesicles or bullae within the epidermis. Most other forms result in pustules. The major pemphigus presentations include: Pemphigus foliaceus , the most common form. Antibodies target the molecules responsible for adhesion between keratinocytes. Middle-aged dogs are most commonly affected and lesions often start on the face and ears, fluctuate in severity and extend to include the rest of the body, especially feet and groin. Most common lesions are macules progressing to pustules and crusts with erosions. Nikolsky sign may be present. Cause is often unknown but may be induced by infections, neoplasia or drug administration. Pemphigus vulgaris is a less common and aggressive form. Lesions may be seen at any age and most commonly occur as vesicles, bullae, ulcers or erosions at mucocutaneous junctions and in the mouth. Lesions may also be present in other skin areas. Nikolsky sign may be present. Pemphigus erythematosus is less common with erythematous, pustular, crusting lesions generally appearing on the face and ears. Loss of pigment on the nose may be seen more often in this presentation, allowing ultraviolet light to aggravate lesions. Pemphigus vegetans is very rare in the dog. Diagnosis is based on clinical signs, biopsies with histopathology, and immunofluorescence studies. Treatment involves administration of appropriate immunosuppressive agents. Prognosis varies with disease severity.

Perianal Fistulae

A painful, chronic and progressive disease of the tissues surrounding the anus and rectum. The disease may affect adult dogs of any age and is most frequently seen in German Shepherd dogs. Primary lesions are ulcerations and sinus formation of varying size and depth. Presenting signs could include straining to defecate, constipation, increased frequency of defecation, diarrhoea, reluctance to elevate the tail (painful), excessive licking around the anal region or systemic signs such as weight loss and lethargy. Differential diagnoses include perianal neoplasia, cellulitis secondary to anal gland disease, or deep regional pyoderma. Diagnosis is through histopathology. Treatments vary and may include immunomodulatory or immunosuppressive medications. Use of some medications may be extra-label.

Perianal Gland Tumours

A group of common hormone-responsive tumours in the dog. Most arise from the circumanal glands (less frequently from anal sac glands). Cause is unknown. Tumours tend to occur in older dogs (11+ years) and may be found next to the anus, on the tail, perinueum, prepuce, thigh, or dorsal lumbo-sacral area. Lesions are generally firm and located in the dermal and epidermal tissues on palpation. They may or may not be well circumscribed. Reported circumanal tumours include hyperplasia, adenomas, and carcinomas. Most of these may be benign however larger lesions are reported to be at increased risk of metastasis and carcinomas tend to grow more rapidly. Most anal sac tumours are adenocarcinomas and tend to metastasise to regional lymph nodes giving a poor prognosis. Hyperadrenococrticism may increase the likelihood of tumour occurence in females or recurrence in treated male dogs. Treatments include surgical excision, castration of entire male dogs (high success rate for hyperplasia and adenomas), and cryotherapy or radiotherapy.

Petechia

A small pin-point area of haemorrhage within the skin less than 1 cm in diameter. Will not blanch with diascopy.

Phosphodiesterase inhibitors

The most common phosphodiesterase inhibitor reportedly used in canine dermatology is pentoxifylline, a synthetic xanthine derivative (related to caffeine and theophylline) which may be considered for its immunomodulatory properties. Pentoxifylline may have multiple immunomodulatory effects including anti-inflammatory activity, inhibition of T and B-cell proliferation and inhibition of natural killer cell function. The drug has been considered for several immune mediated diseases (e.g. autoimmune disease , contact allergies or atopic dermatitis ). Additionally the drug has been considered for use in non-healing wounds, deep scarring lesions, and vasculopathies. Use in dogs may be extra-label.

Pigmentation

The presence of melanin or pigment within the skin. Amount of pigmentation may be influenced by genetics and by trauma or lesions within the skin. Melanocytes (pigment producing cells) are mainly located in the basal layer of the epidermis but also in the superficial dermis and in the cells surrounding hair follicles, sebaceous glands and sweat glands. An increase in pigment is called hyperpigmentation , a decrease is called hypopigmentation .

Plaque

A primary lesion of the skin which appears as a large, flat-topped elevation greater than 1cm diameter which can be palpated as a solid mass. Formed by either the expansion of individual papules or merging of several neighbouring papules.

Plasma cells

Mononuclear white blood cells which evolve from B-cells following exposure to their target antigen. Plasma cells are responsible for production of immunoglobulins (antibody response).

Pododermatitis

Pododermatitis ('interdigital pyoderma') is inflammation of the skin of the foot. Affected tissues may include interdigital spaces, foot pads, nail folds (paronychia), claws, or other tissues of the foot. There are many potential causes and therefore presentations of inflammatory foot disease.

Polymerase Chain Reaction Assays

A highly sensitive diagnostic technique which enables the detection of very small amounts of specific DNA (or RNA) sequences. The technique involves recognition and replication (or amplification) of a target sequence which is specific to the test organism. PCR tests are most commonly used to identify micro-organisms which are difficult to isolate or culture (e.g. viruses, Mycobacteria, ERLICHIA) but may also be used to identify specific genetic conditions, or malignancies. Sampled tissues may include, for example, blood, swabs, or faeces depending on the suspected disease process.

Provocation test

A diagnostic test used to identify potential hypersensitivity reactions. This may include intradermal testing , patch testing , or re-exposure to an allergen which has been avoided for a period of time (e.g. food elimination trial or avoidance trial for contact allergies).

Pruritus

Itching.

Pseudomonas

A gram negative rod-shaped anaerobic bacterium . Can be present on the skin surface without resulting in disease but may act as a secondary invader of skin lesions.

Pustule

An accumulation of purulent material within the epidermis.

Pyoderma - Superficial vs. Deep

Superficial bacterial pyoderma is a bacterial infection of the epidermis and follicular epithelium. Common examples include impetigo, mucocutaneous pyoderma, and superficial bacterial folliculitis. Deep pyoderma is a serious infection which occurs in tissues deeper than the hair follicle potentially including the dermis and subcutis. Affected animals may show signs of systemic illness and lesions very often result in scarring. Infection penetrating to this depth indicates an initial deep trauma or underlying disease. Often occurs as a progression of a superficial pyoderma. Speed of progression of infection may be increased by severe tissue trauma (self-trauma, severe demodicosis) or immunosuppression (from disease or medication). Examples include progressively deep folliculitis, furunculosis and cellulitis as well as subcutaneous abscesses.

Pyotraumatic dermatitis

Also called hot spot. A bacterial skin disease (usually surface or superficial skin disease) which occurs secondary to a skin trauma (e.g. scratch or wound). Disease is acute in onset with well demarcated, reddened, moist exudative lesions and alopecia.

Pyrexia

Abnormally elevated body temperature (fever). Normal temperature in dogs is approximately 39°C (102°F).

RAST

A diagnostic blood test which measures the amount of allergen-specific IgE present. The test surface contains the test allergen and is incubated with the animal's serum sample. If specific IgE is present it binds to the allergen. A radio-labelled secondary antibody solution is added which binds to any specific IgE, if present. The amount of radioactive iodine marker (and therefore allergen specific IgE) can then be measured.

Sarcoptes scabies

The canine scabies mange mite. Mites burrow in the epidermis creating an extremely pruritic dermatitis. Female lays eggs in skin tunnel which develop into larvae, then moult through 2 nymphal stages before becoming adults. Mites are highly contagious with lesions seen most commonly on pinnae (especially ear margins), lateral elbows and hocks. Spread from these areas generally progresses to the head and ventral trunk before becoming generalised. Lesions include redness (erythema), pupaules, alopecia and small haemorrhagic crusts. Pruritus leads to self trauma (excoriations) with secondary bacterial infection common. If disease becomes chronic the skin becomes thickened ( hyperkeratosis ), corrugated and hyperpigmented , and lymph nodes may become enlarged. Diagnosis: A positive pinnal-pedal reflex is considered indicative. Definitive diagnosis is achieved by identifying mites on skin scraping. Scraping should be deep enough to include full thickness of the epidermis (tinged with blood). A sarcoptes IgG ELISA test is also commercially available. False negatives may occur early in the disease process where dogs have not yet seroconverted. False positives may occur with atopic dermatitis as the test will cross react with house dust mite allergy. Eggs are about 230um long and ellipsoid. Larvae have 6 legs, nymphs and adults have 8 legs and area about 0.5mm long (visible at low power on compound microscope). Response to treatment may also be considered diagnostic. Treatment includes control of secondary infection and treatment with an appropriate acaracide. Pet owners can potentially develop a severely prurituc, papular rash if in contact with infected dogs.

Scabies

An inflammatory skin condition caused by sarcoptid mites. Also known as sarcoptic mange (see Sarcoptes scabies) or fox mange.

Scale

Thin flakes of cornified cells which are shed from the surface (or horny) layer of the epidermis. The shedding of skin cells which occurs normally with cell turnover is not generally visible as cells are not lost in clumps. Normal cell turnover is approximately 21 days. With increased rate of production, clumps of poorly differentiated cells may be shed (seen as scale). Scale may vary in appearance and in consistency, from dry (see dandruff) to oily. Altered rate of keratinisation can also affect sebaceous gland function resulting in an increase in oily or greasy secretions (see seborrhoea). Scale may be a primary lesion (for example in colour dilution alopecia) or may be a secondary feature of many inflammatory skin conditions such as hypersensitivities, bacterial skin disease, endocrine (hormonal) disease, and disease caused by ectoparasites.

Scar

A secondary skin lesion, i.e. one which is seen after skin trauma or skin lesions. Fibrous tissue replaces damaged dermis or subcutaneous tissue (i.e. deep skin lesions). The area is often hairless (alopecic), and either depigmented (most common) or hyperpigmented (e.g. in dark skinned dogs). Fibrous tissue contracts creating a shrunken or atrophied appearance to the skin.

Sebaceous cyst

A non-neoplastic, enclosed sac or capsule within the skin filled with sebaceous secretions which occurs as a result of blockage of the sebaceous duct (or outlet).

Sebaceous Gland Tumours

Common neoplasms in the dog. Tumour types include Nodular sebaceous hyperplasia, the most common form which usually appears as a solitary, well circumscribed, wart-like lesion which may appear greasy, pigmented or ulcerated. Most common on the limbs, trunk and eyelids of smaller breeds such as Poodles, Beagles and Dachshunds. Sebaceous epithelioma is the next most common and of similar apperance to nodular sebaceous hyperplasia. Most commonly seen on the head or eyelids of long-coated breeds such as Malamutes, Irish setters, Shih tzus or Lhasa apsos. Sebaceous adenomas are less common, appear similar to the more common sebaceous tumours and tend to occur on the eyelids and limbs. Sebaceous carcinomas are the least common, they are more nodular in appearance and often ulcerated. Lesions are most frequent on the head and limbs. Diagnosis is by biopsy and histopathology, treatment ranges from surgical excision to observation. Metastases of these carcinomas are rare.

Seborrhoea

A chronic skin disease characterised by a keratinisation abnormality resulting in scale formation, greasiness of the skin and coat, and occasionally secondary inflammation. Clinical features may vary from dandruff to greasy scales and crusts which accompany inflammation. Seborrhoea sicca (dry seborrhoea) is a dry scaly seborrhoeic dermatitis. Skin and coat are dry. Seborrhoea oleosa (oily seborrhoea) is a moist, oily seborrhoea with exudative crust formation. Skin has a strong rancid odour. Seborrhoeic dermatitis involves scaly and greasy skin and coat associated with inflammation. Seborrhoea may be a primary condition (e.g. a congenital disorder called 'dirty puppy syndrome') or secondary to inflammatory skin conditions, endocrine disorders, nutritional deficiencies, or environmental factors such as excessive bathing. Treatment of secondary seborrhoea involves identification and management of the underlying disorder. Testing for Malassezia , which may cause or exacerbate the condition is recommended for dogs with seborrhoeic dermatitis. The skin condition may also be managed with antiseborrhoeic , hypoallergenic, or moisturising shampoos depending on the skin condition. Moisturising hypoallergenic shampoos would be used for dry seborrheoa where stripping shampoos such as benzoyl peroxide would be avoided. Oily seborrhoea may be treated with antiseborrhoeic shampoos. All shampoos are used on an as-needed basis as over-use can dry the coat and cause seborrhoea.

Serology

In vitro (outside the body, in an artificial test environment) measurement of antibody-antigen reactions. Common examples in dermatology include ELISA testing and RAST.

Skin fold dermatitis

"Intertrigo', a surface bacterial skin infection resulting from skin trauma due to frictional rubbing of one skin fold against another. Increased humidity between skin folds may also predispose to infection Forms of skin fold dermatitis include: Lip fold, Facial fold, Vulval fold, Tail fold, and Body fold.

Skin scraping

A diagnostic procedure for sampling the skin surface, epidermis and upper dermis. Both deep and superficial skin scrapings may be used. Deep skin scrapings are required for identification of Demodex mites.

Skin tags

Fibrovascular papillomas. Uncommon benign tumours of the skin. Large and giant breed dogs appear predisposed. Cause unknown, may be response to trauma or localised furunculosis. Generally lesions are seen on the trunk, sternum, and bony prominences (such as elbows). There may be one or more lesions present which range in appearance from smooth to rough (hyperkeratotic), 2 - 5 mm in diameter and 10 - 20 mm in length. 'Tag' may have a narrow stem (pedunculated) or appear finger like (filiform). Degree of pigment varies. Diagnosis is via histopathology (biopsy). Treatment ranges from monitoring to surgical excision.

Smear

A sample obtained (of tissue or fluids) for examination under a microscope. Material is spread thinly across the slide with a swab , loop, or another glass slide to allow examination of cell types or for micro-organisms such as bacteria and protozoa.

Solar dermatitis

A chronic inflammatory reaction in the skin caused by long term exposure to sunlight. Condition is more common in sunny climates and in white-coated animals. The skin has multiple barriers to protect against damage from ultraviolet light. A thick haircoat offers significant protection as does melanin pigment within the skin. Solar dermatitis lesions are more commonly seen in white or light-skinned animals and in areas where the coat is thinned (such as tips of ears, nose, eyelids and ventral abdomen). These physical barriers may also be reduced if skin has been damaged through injury or disease resulting in alopecia (hair loss), scarring and depigmentation. The remaining physical barriers within the skin such as the outer layer of the epidermis (stratum corneum) or blood within the skin are easily overcome by prolonged and repeated exposure to sunlight. Ultraviolet light can trigger a range of chemical reactions within the skin triggering changes such as increased cell proliferation, cell mutation and cell toxicity. Generally seen in summer (or winter from snow reflections), initially skin becomes reddened (erythematous) and scaly. With continued exposure, loss of hair around the lesion further exposes skin to UV damage. Lesions ooze exudate which crusts and ulceration may occur. Long term damage leads to scarring, fissure formation and development of skin neoplasia such as squamous cell carcinoma through cell mutation. Diagnosis is based on typical lesions occuring in exposed white or pink skinned areas, with surrounding pigmented skin being unaffected. Where scarring is observed, it is important to rule out an underlying skin condition which has predisposed to solar dermatitis through loss of pigment. Skin neoplasia should be considered with severe skin lesions such as ulcerations and fissures within the skin. Diagnosis is confirmed on skin biopsy. Treatment includes photoprotection and anti-inflammatories such as glucocorticoids if required. Exposure to sunlight (direct or reflected) should be avoided during high risk hours of 9am - 3pm. Sunblock or sunscreen may be applied. In some cases supplementation with carotenoids or surgical intervention may be considered (e.g. feline ear lesions). Also called actinic dermatitis, canine nasal solar dermatitis (collie nose), feline solar dermatitis (typically ears, nose and eyes of white cats).

Spongiosis

A histopathology term describing oedema of the intercellular spaces of the epidermis, creating a spongy appearance. A common feature of many subacute or acute inflammatory skin conditions.

Squamous cell carcinoma

A common malignant form of skin neoplasm (tumour). The tumour originates from keratinocytes in the epidermis. These tumours occur most frequently in sun-damaged skin. In dogs, the papillomavirus may also be associated with development of squamous cell carcinomas. Tumours are generally seen in older dogs and are most commonly found on the trunk, limbs, nose, lips, anus, digits and scrotum. Lesions may appear ulcerated or may develop as proliferative raised lesions in the skin. Dark coated dogs are more likely to develop tumours of the nail bed, light-coloured, thin-coated dogs are more likely to develop tumours due to sun damage. Diagnosis is by cytology and histopathology. Treatment often involves surgery, or radiotherapy.

Staphylococcus intermedius

A gram positive coccus bacterium commonly found on the skin. The most common bacteria present in superficial pyodermas . Some dogs may develop a hypersensitivity (allergic) reaction to Staphylococcus intermedius antigens.

Suppurative

A term used to describe the discharge of pus from a lesion.

Swab

A term most commonly used to describe a cotton-tipped applicator which may be used for applying medications or obtaining samples or cells or secretions from body tissues for cytology or culture. Terms such as 'Ear swab' or 'vaginal swab' for example, may be used to describe the process of obtaining a sample from the described area with a sterile cotton-tipped applicator for cytology or culture.

Tail gland hyperplasia

A keratinisation defect affecting a highly glandular area of skin on the dorsum of the tail called the 'tail gland' in both cats and dogs. In both species the area of skin is differentiated from the surrounding skin by the presence of simple hair follicles, many large sebaceous and circumanal glands as well has a large number of epitrichial sweat glands. In dogs the tail gland is an oval area on the dorsal surface of the tail approximately 2.5 - 5.0 cm from the tail base. Cell hyperplasia may occur with primary or secondary seborrhoea , or as a result of elevated blood androgen levels where hyperplasia of circumanal glands around the anus and other regions of the body may also be present. Clinical signs: Tail hair may initially mask the early signs of hyperplasia, but friction over the area or pressure from hyperplastic cells on the hair follicles may result in hair loss. Underlying skin may show any / all of scale , greasiness and hyperpigmentation . Secondary infection is rare, appearing as acne -like gland infection. Advanced cases may appear nodular either due to uneven hyperplasia, cyst formation or infection. Treatment: Signs are often cosmetic only with no treatment required. In dogs with elevated androgen levels castration (surgical or chemical) may result in an improvement within 2 months. Secondary infection is treated by lancing of pustules and administration of systemic antibiotics .

Telogen

Part of the cycle of hair growth. Telogen describes the period of rest or inactivity of the hair follicle. On epilation, the root or bulb of the hair appears rough, non-pigmented, with a club or spear-shaped appearance. The normal haircoat generally consists of hairs in either anagen (active growth) or telogen phase. Intermediate catagen hairs are less commonly found.

Therapeutic Trials

Administration of trial therapy to diagnose or rule-out suspected disease. Therapeutic trials may be used where diagnostic tests are inconclusive or unavailable (e.g. acaricide treatment for suspected sarcoptic mange ) or as part of a methodical approach to treatment of dogs with multifactorial skin disease (e.g. bacterial infection , fleas , and atopic dermatitis ) in order to reduce pruritic flare factors .

Tick

Ticks are obligate parasites of the acarine family. There are many species around the world, each with a different geographic distribution. Ticks are either 2-host or 3-host parasites. Eggs are laid by females in the ground. Each subsequent stage of the life cycle (larvae, nymphs and adults) climb on to a host to feed before dropping to the ground to moult (or to reproduce as adults). Ticks feed on blood and lymph, and tick bites may cause skin irritation. Several tick species have a neurotoxin in their saliva which may cause paralysis in the host. Ticks can also act as vectors for many pathogenic diseases. Examples include Rickettsia spp (e.g. Rocky Mountain Spotted fever), or Borrelia (e.g. Lyme disease). Other common tick species include Amblyomma, Dermacentor, Haemaphysalis and Ixodes species.

Toxic epidermal necrolysis (TEN)

A rare disorder of the skin and oral mucosa which is commonly (but not always) associated with drug hypersensitivity. Characterised by an acute onset of systemic signs (pyrexia, anorexia, lethargy and depression) and multifocal or generalised skin lesions. Vesicles and bullae, necrosis and ulcers with epidermal collarettes may be found.

Transmissible Venereal Tumour (TVT)

A transmissible but uncommon neoplasm (tumour) of the dog. Degree of malignancy varies. Transmission most commonly occurs during mating, but may be transmitted to other areas of the body via self grooming or trauma such as licking, biting, or scratching. T-cells, B-cells and plasma cells are responsible for immunity against the neoplastic cells, resulting in tumour regression. Immunosuppression allows increased rate of tumour growth, and maligancy. Lesions are seen in mature, sexually active animals, particularly those living in areas with a large number of free-ranging dogs. Lesions are most commonly found on the external genitalia and skin (especially face and limbs).Number of lesions, shape, consistency, size, and depth of lesion varies. Ulceration of lesions is common. Genital discharge may be present (often haemorrhagic), and lesions in this area may be fragile and haemorrhagic. Metastases may occur to lymph nodes, skin, or any other body part. Diagnosis is by presentation and histopathology. The most successful treatment option is chemotherapy.

Trichogram

A diagnostic test which provides information on the hair root, shaft and tip. This can be used to differentiate alopecia resulting from grooming from that resulting from disease in the hair follicle. Evidence of trauma to the hair shaft with broken ends may indicate over grooming as compared to a normal hair shaft with a finely tapered tip. Examination of the hair shaft may also provide clues as to pathology occurring within the hair follicle (such as uneven coloration of the hair shaft due to uneven distribution of melanin granules in colour dilution alopecia ). Technique: A small sample of hair is plucked with fingers or forceps and either fixed to clear adhesive tape which is adhered to a microscope slide, or placed directly on a microscope slide with mineral oil and a cover slip. The slide is examined under the microscope. In addition to the structure of the hair shaft, trichograms may also reveal the presence of parasites such as Demodex mites or lice eggs (nits), or the presence of dermatophyte hyphae and/or arthrospores.

Trombicula

Trombiculid mites (harvest mites, chiggers) include several species of mite of which the larval stage is the only parasitic stage. Adults scavenge on decaying vegetable material and may live for about 10 months. Eggs are laid in the ground and hatch into the 6 legged larval parasitic stage. Infection generally occurs around autumn (harvest time). The larvae climb onto low vegetation and attach to passing animals or people. Multiple larvae will fix in one area, attaching with their mouth parts to the surface of the skin. Larvae drop to the ground and moult into nymph stage, maturing into adults. A life cycle is completed in about 50 - 70 days Lesions include pruritus, papules, crust, scaling and alopecia (hair loss) in affected areas. Commonly affected areas include around the eyes, ears, legs, toes, perineal region and ventrum (areas in contact with grass and vegetation). Repeated exposure may result in hypersensitivity reactions. Differential diagnoses include seasonal dermatoses such as atopic dermatitis , or ear mites (orange - red colour of trombiculd mites make them easily differentiated). Diagnosis is based on observation of the red or orange coloured larval stages. If examined under microscope mites should be placed in mineral oil to prevent escape. Treatment involves parasiticide rinses. Reinfestation is common when animals return to their normal environment.

Urticaria

A vascular reaction of the skin usually marked by transient appearance of wheals and often severely pruritic. Also called 'hives'. May occur as part of an immune based reaction (such as type I or Type III hypersensitivity ), following psychological stress, or physical stress (temperature extremes, sunlight, exercise, pressure) or in response to certain drugs and chemicals. Individual wheals may resolve within 24 hours but urticaria may be either acute or chronic. Differential diagnoses include folliculitis , vasculitis , erythema multiforme and neoplasia such as mast cell tumour. Diagnosis is based on history, presentation, identification of trigger. Treatment includes elimination or avoidance of trigger, epinephrine and/or glucocorticoids.

Vasculitis

Inflammation of the blood vessels. Cutaneous vasculitis is an uncommon disorder in dogs and rare in cats. Inflammation causes blood to leak into surrounding tissues (purpura). Haemorrhagic patches are seen as ecchymoses and petechiae in the skin which do not blanch on diascopy , or haemorrhagic bullae. Fluid accumulation in the skin results in oedema, wheals, papules , pustules , plaques and nodules with skin also developing alopecia, scarring, necrosis and ulceration. Lesions more commonly occur on the extremities (such as ear tips, paws), areas of friction (e.g elbows and hocks) and dependant areas (those nearest the ground). Location of lesions may be closely associated with vascular pathways. Skin may be the only organ affected or other systemic signs may be observed (rare). Several different forms or presentations of vasculitis have been reported. Differential diagnoses include other systemic diseases resulting in haemorrhagic skin conditions such as Disseminated Intravascular Coagulopathy (DIC), other coagulopathy (bleeding disorder), or systemic lupus erythematosus . Localised differential may include frostbite in colder climates. Diagnosis is based on history, presenting signs and biopsy. As the condition may be associated with other underlying disease (examples include leishmania , parvovirus, or immune mediated disease such as SLE , drug reactions or hypersensitivities ), investigation for concomitant disease may be required. Treatment includes addressing any underlying cause and administration of immunosuppressive medication (examples reported include pentoxifylline, glucocorticoids and azothiaprine). Treatment should be based on underlying pathology.

Vesicle

A small blister. A primary lesion of the skin which appears as a well circumscribed area of raised epidermis up to 1cm diameter filled with clear fluid. Vesicles are fragile and transient so may be infrequently seen. Blisters greater than 1cm diameter are called bullae. Vesicles may occur in viral or autoimmune skin disease or in response to irritants (chemicals, trauma, burns).

Vitamin A (retinol) responsive dermatosis

An adult onset seborrhoeic skin condition reported in Cocker spaniels and to a lesser degree in Labrador retrievers and Miniature Schnauzers. Dogs develop a seborrhoea which is non responsive to standard treatments. Follicular plugs and hyperkeratotic plaques are seen particularly on the ventral and lateral chest and abdomen. Dogs have a rancid skin odour and may also show signs of crusting, scaling, alopecia and follicular papules. Signs are often accompanied by a characteristically waxy otitis externa . Condition is mildly pruritic. Coat is dry, dull and falls out easily. Generally dogs are otherwise well. An abnormal presentation with pruritus and papular dermatitis in the dorsal regions has been reported. Differential diagnoses include sebaceous adenitis, follicular dysplasia, true Vitamin A deficiency, demodicosis (atypical) and hyperadrenocorticism (generally accompanied by other systemic signs). Diagnosis is through breed, history, presenting signs (particularly extensive follicular plugging) +/- biopsy and rule out of differential diagnoses. Treatment includes management of secondary infections and long term supplementation with Vitamin A (given with a fatty meal).

Wheal

A primary lesion caused by oedema (fluid accumulation) in the skin. Lesion appears as a well circumscribed raised area, either ridge-shaped or rounded and white to pink in colour. Pinkish colour disappears if pressure is applied with clear glass or plastic ( diascopy ). Wheals tend to appear and disappear within minutes to hours. Examples include urticaria or 'hives', insect bite reactions, or positive responses in skin allergy testing. See also angioedema .

Wood's lamp examination

Wood's lamp is a diagnostic tool which produces ultraviolet light. Approximately 50% of the pathogenic dermatophyte species Microsporum canis will fluoresce a bright green colour under ultraviolet light.

Yeast

A form of fungus, some species of which may cause skin disease. Malassezia and Candida are the most common yeast species causing skin disease in dogs.

Zinc responsive dermatosis

A skin condition which improves with zinc supplementation, indicating a deficiency as the underlying cause. Zinc is an important mineral in many critical biological processes within the body. Zinc deficiency is a rare cause of skin disease in dogs. Deficiencies may result from inability to absorb the mineral from the intestine (genetic, chronic enteritis, minerals competing for absorption) or dietary imbalance. Severe deficiencies may result in stunted growth in young animals or poor wound healing. Depending on breed and underlying cause, lesions may vary in their appearance. Hyperkeratosis is common. Two major presentations are described: 1) Erythema, alopecia, crusting, scaling with a supperative dermatitis at body openings (eyes, mouth, chin especially). Lesions may be pruritic. Crusting appears at pressure points. Dogs have a dull, oily coat and may have footpad and claw lesions. Young adults are most commonly affected, especially Siberian Huskies, Alaskan Malamutes and Bull Terriers. 2) Young puppies or adults on zinc deficient diets may may have stunted growth, hyperkeratotic plaques form on pressure points, pads and nasal planum. Large fissues may appear in these lesions. For both presentations, secondary infections may occur. Diagnosis is based on history, physical examination and skin biopsy. Treatment includes zinc supplementation. Duration is for life in dogs with poor absorption, but may be discontinued if dietary deficiency is identified as the cause.

Zoonotic diseases

A disease, parasite or pathogen that may be transmitted from animals to people. Examples include hookworm, cheyletiella, ringworm and Sarcoptes scabies.