Erythema multiforme.

Erythema multiforme is a cutaneous reaction pattern manifested by well-demarcated plaques on the trunk and extremities. Target, or "iris," lesions, with central clearing, are characteristic of this disorder. Erythema multiforme may be a mild condition (erythema multiforme minor), or it may be a severe, possibly life-threatening condition (erythema multiforme major or Stevens-Johnson syndrome). Toxic epidermal necrolysis, manifested by widespread epidermal desquamation, is the most severe form of this disorder. The three most common triggers for erythema multiforme are herpes simplex infection, mycoplasma infection and drug reactions. Drugs that can precipitate erythema multiforme include sulfonamides, penicillins, phenylbutazone and phenytoin. The appearance of the characteristic lesion is usually diagnostic. However, conditions such as tinea corporis, lupus erythematosus, herpetic gingivostomatitis, Behçet's disease and erosive lichen planus, among others, may mimic erythema multiforme. For mild cases, treatment is supportive, with antibiotics used for secondary skin infections. For severe causes, many physicians use systemic corticosteroids, although this treatment is not universally endorsed.