Erythema multiforme (EM) is a skin and mucous membrane disease characterized by an eruption of macules, papules, nodules, vesicles, or blisters with characteristic "bull's-eye" lesions. It is an uncommon disease that presumably is immune-mediated. Most cases are unknown in origin. The most common underlying causes are infections (staphylococcal folliculitis, anal gland sacculitis, bacterial endocarditis), drugs (chloramphenicol, cephalexin, diethylcarbamazine, trimethoprim-sulfonamides), and cancers (bone disorders, splenic tumors). Most cases in dogs have been secondary to bacterial folliculitis or reactions to drugs. The process is associated with keratinocyte cell death, known as apoptosis. The skin eruption is usually acute and often involves the limbs, mouth, armpits, and ears. There are erythematous macules (red spots on the skin), papules (pimples), itchy plaques, small and large blisters, erosions, and ulcerations. Crusting and skin discharge are secondary manifestations.
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Diagnosis is based on history, clinical signs and laboratory findings. The condition is usually difficult to differentiate from lupus erythematosus and ulcerative dermatosis. According to recent changes in the disease classification and identification, erythema multiforme is suspected if patchy lesions with ulcerations are present on less than 10% of the body surface and with more than one mucous membranes affected. If the causative condition can be treated, the disease can be expected to regress spontaneously. Anti-inflammatory doses of prednisolone may be given to decrease the inflammation and itch but are controversial because they can also aggravate some cases. Pentoxifylline has been used occasionally with variable results in recurrent, non-drug associated cases. Azathioprine, sulfasalazine and cyclosporine have also been used as treatments in resistant cases.
- Nesbitt G.E. & Ackerman L.J. Canine Immune-Mediated Skin Diseases. In: Canine and Feline Dermatology: Diagnosis and Treatment. Veterinary Learning Systems, Trenton, New Jersey
- Cutaneous Drug Reactions, Craig K. Svensson, Edward W. Cowen, and Anthony A. Gaspari Pharmacol