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Erythema multiforme (EM) is an acute self-limited, usually mild, and often relapsing mucocutaneous syndrome. The disease is usually related to an acute infection, most often a recurrent herpes simplex virus (HSV) infection. EM is defined only by its clinical characteristics: target-shaped plaques with or without central blisters, predominant on the face and extremities.
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The absence of specific pathology, unique cause, and biologic markers has contributed to a confusing nosology. Recent medical literature still contains an overwhelming number of figurate erythema reported as EM, and the International Classification of Diseases (ICD9) still classifies Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) under the heading of EM.
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The definition of EM in this chapter is based on the classification proposed by Bastuji-Garin et al.1 The principle of this classification is to consider SJS and TEN as severity variants of the same process, i.e., epidermal necrolysis (EN), and to separate them from EM (see Chapter 40). The validity of this classification has been challenged by some reports, especially for cases in children and cases related to Mycoplasma pneumoniae. It has been confirmed by several others studies however, especially the prospective international Severe Cutaneous Adverse Reactions study.2 That study demonstrated that, compared with SJS and TEN, EM cases had different demographic features, clinical presentation, severity, and causes.
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The original name proposed by von Hebra was erythema exudativum multiforme. The term erythema multiforme has now been universally accepted (Box 39-1).
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EM is usually called minor when mucous membranes are spared or minimally affected, for example, lips, and majus (or major) when at least two mucosal sites are involved.
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EM is considered relatively common, but its true incidence is unknown because largely cases severe enough to require hospitalization have been reported. Such cases are in the range of 1 to 6 per million per year. Even though the minor form of EM is frequent than the major form, many other eruptions (including annular urticaria and serum sickness-like eruption) are erroneously called EM.3
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EM occurs in patients of all ages, but mostly in adolescents and young adults. There is a slight male preponderance (male–female sex ratio of approximately 3:2). EM is recurrent in at ...