Veterinary Dermatology: Core Concepts and Clinical Reasoning
Approach to the dermatology patient
Veterinary dermatology rewards a disciplined, problem-based method. The candidate must be fluent in the major categories of skin disease: allergic (atopic dermatitis, food hypersensitivity, flea allergy, contact), infectious (bacterial pyoderma, dermatophytosis, Malassezia), parasitic (Demodex, Sarcoptes, Cheyletiella, fleas, ticks), immune-mediated (pemphigus, lupus, erythema multiforme), endocrine/metabolic (hypothyroidism, hyperadrenocorticism, sex-hormone disorders), neoplastic (mast cell tumor, lymphoma, squamous cell carcinoma), and keratinization/idiopathic conditions. Know that distribution and primary lesion type drive the differential list more than any single test.
Concepts candidates must master
Understand primary versus secondary lesions (papule, pustule, macule, vesicle vs. scale, crust, lichenification, excoriation), and how chronicity alters appearance. Know the diagnostic sequence: history and drug exposure, dermatologic exam, skin scrapings, cytology, trichography, fungal culture, Wood's lamp limitations, elimination diet trials, intradermal/serologic allergy testing, and biopsy with proper site selection (avoid ulcerated or secondarily infected sites; sample primary lesions).
Common traps
Questions often hinge on timing and interpretation: a Wood's lamp is insensitive and not diagnostic; cytology distinguishes bacteria from yeast but not always pathogenicity; a negative scraping does not exclude Demodex (deep scrapings, multiple sites, hair pluck). Another trap is conflating pruritus with allergy-secondary infections cause pruritus and must be resolved before judging response. Endocrine diagnoses require confirmatory testing, not pattern recognition alone.
Worked rule of thumb
A young dog with non-seasonal pruritus, otitis, and pododermatitis: build an allergy list, treat secondary pyoderma/Malassezia first, then reassess pruritus. If pruritus persists after infection control, pursue diet trial and allergen testing in sequence rather than simultaneously-control one variable at a time.