Erythema multiforme (EM) is an acute, self-limited disorder of skin and less so of the mucous membranes. It is characterized by the onset of oval or round, fixed, erythematous skin lesions which appear symmetrically on the skin and remain at the same site for at least 7 days and often for 2 or 3 weeks. The lesions advance over several days to form concentric zones of color change in which the central zone of epidermal injury becomes dusky, blistered, or crusted which are known as target or iris lesions. EM lesions can be recurrent when preceded by a lesion of herpes labialis. Initially skin lesions involve the dorsal surface of the hands and the extensor surfaces of the extremities. Palms and soles are frequently affected with lesser involvement of flexor aspects. When mucosal lesions are involved it is limited to the only the oral mucosa, and lesions are few (5 to 10) in contrast to hundreds on the skin

Differential diagnosis

Diagnoses confused with EM include acute urticaria, and other oral mucous lesions. Acute urticaria can be distinguished from EM by its transient nature. EM has crusting or blistering in the center in the stead of pale edema in the center that is found in urticaria.

Pathophysiology

EM is thought to be due to host response to herpes simplex virus (HSV) antigens expressed on keratinocytes within the target lesion. In a few children where HSV may not be the precipitating agent, Epstein-Barr virus, cytomegalovirus, and other human herpes viruses have been implicated.

Treatment

Symptomatic relief may be obtained from wet compresses or oral antihistamines. In children with recurrent EM prophylaxis with oral acyclovir may be considered.