Erythema multiforme.

Erythema multiforme (EM) is an episodic, variable, self-limited, and often recurrent inflammatory disorder of the skin and mucous membranes. In this article a definition of EM is proposed, its known clinical and histopathologic spectrum is reviewed, an approach to diagnosis and treatment is suggested, and documented evidence regarding its etiology and pathogenesis is presented. EM would appear to be a hypersensitivity reaction to a variety of precipitating agents. It has been directly linked to Mycoplasma pneumoniae and herpes simplex virus infections and possibly is triggered by a number of other infectious agents and by certain drugs. Accumulating observations of diverse immunologic phenomena suggest an underlying immune mechanism of as yet unclear type. Future investigation should be directed toward defining diagnostic criteria, evaluating reported etiologic associations, and clarifying the immunologic basis of this complex and enigmatic disorder.