Erythema multiforme was first documented in the dog in 1983 and in the cat in 1984.
The pathomechanism of erythema multiforme is unclear. It is an inflammatory reaction pattern of the skin and mucous membranes
characterized by distinctive clinical and histopathological findings. It has been associated – usually circumstantially –
with a wide variety of triggering factors in veterinary medicine. It is hypothesized that erythema multiforme represents a
host-specific cytotoxic (T-lymphocyte) immunologic attack on keratinocytes expressing nonself antigens. The antigens involved
are predominantly microbes and drugs.
Proposed etiologic factors for erythema multiforme in dogs and cats are listed in Table 1.
Table 1. Etiologic Factors for Erythema Multiforme in Dogs and Cats
Erythema multiforme is uncommon-to-rare in dogs and cats. It accounted for 0.4% of all the canine dermatological conditions
examined at a university clinic. The most common presentation is an asymptomatic maculopapular eruption or a variably symptomatic
vesiculobullous and/or ulcerative eruption. Lesions are typically acute in onset and more-or-less symmetrical. The most commonly
affected body sites are the ventrum (especially axillae and groin), mucocutaneous junctions, oral cavity, pinnae, and pawpads.
Lesions may be painful, but are rarely pruritic. Systemic signs of illness may include depression, lethargy, anorexia, pyrexia.
Diagnosis is confirmed by biopsy and appropriate tests/withdrawal procedures to address suspected etiologic factors in Table
Treatment includes management/elimination of known triggering factors (Table 1), and immunomodulatory drugs.Drugs that may
be useful in erythema multiforme include: (a) systemic glucocorticoids; (b) pentoxifyilline (dog); (c) azathioprine (dog);
cyclosporine(5 mg/kg q24h with food); intravenous human immunoglobulin.
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