DERMATOLOGY SKIN DISEASE: APPROACH TO DIAGNOSIS

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1 DERMATOLOGY SKIN DISEASE: APPROACH TO DIAGNOSIS History Clinical Examination List and Prioritise Differentials Diagnostic Testing/Trials (eg Treatment Trial) Correlate All Findings History Signalment age, breed and sex Specific History includes: o Presenting Complaint for example pruritis (itch), alopecia (hairloss) o Time Factors age of onset, duration, progressive or recurrent nature o Initial Lesions types and sites o Presence of Pruritis sites and degree o Previous Treatment drugs and response to drugs Non-Specific History o Regular Routine bathing, flea control and diet o Activity amount of exercise and whether the animal is a pet, working animal, used for show or agility o General Health Clinical Examination Skin lesions may be primary or secondary Primary Lesions produced by disease, and are often sparse or absent Secondary Lesions produced by other processes (eg secondary infections or self trauma), and are more common Pustule Papule Description DDx Images Primary Lesions Small, circumscribed, whitetopped elevation filled with pus. May be either: Intraepidermal Subepidermal Follicular Pustules are collections of neutrophils within a cavity in the dermis, often surrounded by a ring of erythema Small, solid, palpable elevation of skin up to 1cm in diameter. Papules are caused by: Inflammation or oedema in the dermis Oedema or hypertrophy of the epidermis (SBP) (PF) Parasitic Sarcoptes Oother Mites Flea Bites Allergic Flea Bite Allergy

2 Wheal Small, transient circumscribed elevation/raised oedematous area (frequent in dogs and horses, rare in cats) Wheals will pit with digital pressure (AD) Contact Reaction Insect Bite Reaction Adverse Food Reaction Vesicle or Bulla Epidermal Collarette Small, circumscribed fluid-filled elevation of the epidermis Vesicles larger than 1cm are called bullas. These are fragile and transient Circle of scale with a rim of surrounding erythema Pustules typically develop into collarettes (forming the remnant) Bullous Pemphigoid Epidermolysis Bullosa Pemphigus Vulgaris (PV) Secondary Lesions Well Complete Poorly Patchy Hairloss. The degree of alopecia is important and will determine DDx., Demodicosis and Dermatophytosis produce other changes such as pustules or papules. Quiet pyoderma (alopecia without other changes) indicates hormonal disease Less Specific and less useful clinical sign Areata Hormonal Hypothyroidism (HT) (HA) Sec Hormone Cosmetic Hairloss Group Behavioural/Physical Trauma Allergies from licking Self Trauma Sarcoptes

3 Poorly Patchy Barbered Hair is present but shortened in certain areas Self Trauma due to Allergies: Flea Bite Hypersensitivity Adverse Food Reaction Poorly Diffuse Partial Non-pruritic lesions. Coarser and finer coat suggest hormonal differentials Hormonal Imbalance Hyperthyroidism Sex Hormone Imbalance Cosmetic Hairloss Group Erythema Redness Epitheliotropic Lymphoma Allergies Food Adverse Reaction Mallasezia Dermatitis Scaling Lichenification and Greasiness Excessive stratum corneum on the surface. Occurs due to increased speed of cell turnover as cells are unable to desquamate off the surface fast enough Seborrhoea describes scaling when there is programming of cell growth that is too fast Thickening and hardening of the skin, characterized by exaggeration of superficial markings Secondary Infections (MD) Chronic Inflammation Allergies Cheyletiella Infestation Fatty Acid Deficiency Hormonal Imbalance Epitheliotropic Lymphoma

4 Hyperpigmentation Depigmentation Increased pigmentation due to increased melanin deposition Blue depigmentation indicates possible DDx DLE Pemphigus Erythematosus Vitiligo Chronic Inflammation Mucocutaneous (SBP) Neoplasia Epitheliotropic Lymphoma Discoid Lupus (DLE) Pemphigus Group (PF, PE) Excoriations, Erosions and Ulcers Crusting Comedones Defect within the skin (differentiated by the depth of damage in the skin) Multifocal disease is not explained by self trauma Presence of crusting indicates likelihood of immune mediated disease Part of the healing process as a non-specific change Self Trauma Vasculitis Erythema multiforme (EM) Pemphigus Foliaceus shallow crusts DLE deep crusts Mucocutaneous SBP shallow or surface infection Hormonal Hyperthyroidism Sex Hormone Cosmetic Hairloss Group Figure 1 Left to Right: Superficial Bacterial, Pemphigus Foliaceus, Atopic Dermatitis, Epitheliotropic Lymphoma.

5 Diagnostic Tests and Trials A. Surface Skin Cytology Adhesive Tape Impression Dry Swab Impression Smears Dry cotton swab Glass slides Diff Quik Stain Microscope w/oil immersion Equipment Adhesive tape Glass slide Blue dye (Diff Quik or methylene blue) Microscope w/ oil immersion Indications Definitive Diagnosis of Superficial Also diagnostic for: (Tape Squeeze) Surface dwelling mites (cheytiella) Immune-mediated diseases Sample Sites Technique Microscopic Examination Dry areas of alopecia, erythema, scaling or crusting Moist areas at tricky sites (skin folds) Standard tape impression: 1. Push tape onto affected skin several times until adhesiveness reduces 2. Push tape firmly onto class slide sticky side down 3. Curl the tape to allow staining 4. Stain with Diff Quik 1&2 with 6x1 second dips each 5. DO NOT USE FIXER 6. Wash tape under water and uncurl it to lie flat Squeeze tape impression: Place tape onto representative skin Squeeze the tape and underlying skin Repeat for multiple locations Lie the tape on a glass slide, stretching it out NO STAIN OR OIL APPLIED Ear cytology Skin surface (less sensitive than tape impression) Glass slide Diff Quik stain Microscope w/oil immersion Moist, exudative skin sites Potential organisms, inflammatory cells or neoplastic cells Diagnostic for: Fungal Infection Suggestive of: SCC on ulcerated nonpigmented site Inflammatory or neoplastic process Eosinophilic process - allergic or parasitic Ear canal Moist skin with alopecia, exudation, erosions, ulceration or crusting Greasy sites Draining tracts clean the surface and express fresh discharge for sampling 1. Roll the dry swab vigorously onto the ear canal 2. Roll the swab onto the glass slide 3. Stain as per impression smears Scan on low power for clumps of inflammatory cells. Under oil immersion look for bacteria or other pathogens: Intracellular bacteria indicate SBP Malassezia are visible under 40x and 100x but are not associated with inflammatory cells 1. Clean the skin with salinemoistened swab (if exudate present) 2. Push glass slide onto skin and hold for 2-3 seconds 3. Air dry slide and fix (1 st Diff Quik pot) 4. Stain slide 10x scan for clumps of inflammatory cells 40x scan for malassezia, fungal hyphae and spores, inflammatory cell types 100x oil scan for bacteria