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With the wide diversity of cutaneous autoimmune dermatoses, there are multiple clinical signs; whilst there is no singular “pathognomonic” sign that conveys a cutaneous autoimmune disease, the clinician may identify alopecia, crusting (e.g., pemphigus foliaceus), erythema and purpura (e.g., vasculitis, erythema multiforme), ulcerations (e.g., vasculitis, lupus/lupoid variants), and vesicles (e.g., bullous skin diseases). The gold standard for diagnosis of autoimmune dermatoses is biopsy with histopathologic evaluation by a dermatopathologist. Multiple punch biopsies should be obtained from representative lesions; if present, areas of crusting and pustules should be biopsied for examination. Additionally, individual crusts can be submitted for evaluation for such diseases such as pemphigus. Selected sites should not be clipped or scrubbed as this can remove crusts, possibly adversely affecting results. Ideally, animals should not be on corticosteroids when biopsied, and submission of only ulcerated tissue is discouraged, as the outcome may result in an obscure diagnosis of “ulcerative dermatitis”. Special stains, including Periodic acid-Schiff (PAS), may be useful in evaluating for other mimickers, such as dermatophytosis. Additional diagnostic considerations include cytology, dermatophyte culture, antinuclear antibody test (ANA), and tick titers. Cytology is invaluable in supporting or refuting a diagnosis of an autoimmune disease; e.g., the presence of acantholytic keratinocytes surrounded by neutrophils is highly suggestive of pemphigus foliaceus . However, staphylococcal infections and dermatophytes, especially Trichophyton spp., can also induce acantholysis. It is therefore important to evaluate for such agents and treat appropriately, if present. If bacteria are present, a 4-6 week course of systemic antibiotics should be instituted, and if resolution is noted, then a diagnosis of mucocutaneous pyoderma is supported. Note that for discoid lupus erythematosus, the clinical signs and histopathologic changes can very closely resemble mucocutaneous pyoderma of the nasal planum (3). ANA titers, as well as histopathologic analysis, can be helpful in supporting the diagnosis of systemic lupus erythematosus. Additional tests include immunofluorescence or immunohistochemical testing; direct immunofluorescence and immunohistochemical testing (often limited to specialist veterinary immunopathology laboratories) frequently requires special tissue handling, whilst indirect immunofluorescence testing on serum to detect the presence of circulating autoantibodies has shown more promise recently. ■ Treatment With autoimmune/immune-mediated dermatoses, there are two therapeutic approaches that can be utilized for treatment: immunosuppression or immunomodulation .
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