Which dermatologic findings in dogs and cats should prompt workup for underlying systemic disease?

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Accepted Answer

Dermatologic findings that should prompt systemic workup fall into several high-yield categories: severe ulcerative or multifocal nodular lesions, concurrent signs of systemic illness, and specific lesion patterns associated with known endocrine or immune-mediated diseases. The skin is a reliable external marker of internal disease, and early recognition of these patterns maximizes patient outcomes.1 Alopecia, scaling, erythema, and mild crusting — with or without pruritus — are the most diagnostically challenging presentations. Hypersensitivities and infectious dermatoses are the most common causes, but systemic disease underlies these changes in a meaningful subset of cats and dogs.1 Noninflammatory lesions with alopecia are the most common cutaneous pattern of systemic dermatoses across species.8 Specific systemic diseases with well-characterized cutaneous manifestations include hypothyroidism, hyperadrenocorticism, hepatocutaneous syndrome, and systemic lupus erythematosus. Any dog or cat presenting with skin disease and signs referable to these conditions warrants a complete physical examination and systemic diagnostics, not dermatologic workup alone.3 Autoimmune disease should be suspected when cytology reveals sterile neutrophilic inflammation alongside acantholytic keratinocytes (AKs). AKs are large, round, and basophilic; their presence alongside neutrophilic inflammation is characteristic of superficial pemphigus. Skin biopsy is required for definitive diagnosis of any suspected autoimmune dermatosis.4 The dermatologic minimum database — impression cytology, skin scraping, and ear cytology when ear disease is present — is the required first step in every dermatologic workup. Skipping cytology risks misdiagnosis, ineffective treatment, and loss of client confidence.4 When cytology findings are inconsistent with a primary dermatologic diagnosis, systemic evaluation is indicated. In older or clearly debilitated patients, the threshold for systemic workup shou