Erythema Multiforme

Erythema multiforme (EM) is a skin eruption that presents with target lesions. It is an acute, self limited, recurrent disease that affects the skin and mucous membranes and is most often associated with herpes simplex virus. Males are affected slightly more often than females. Most patients are under 40 with 20% occurring in children and adolescents.

A common cause of erythema multiforme is herpes simplex infection. As with oral herpes simplex, EM may be precipitated by exposure to sunlight. Other proposed causes include orf and histoplasmosis.

In EM, there may be no prodrome or a mild upper respiratory tract infection. The rash starts abruptly, usually within 3 days. It starts on the extremities, being symmetrical and spreading centrally. Half of children with the rash have recent herpes labialis. It usually precedes the erythema multiforme by 3 to 14 days but it can sometimes be present at the onset.

The iris or target lesion is the classical feature of the disease.

Initially there is a dull red flat spot or wheal that enlarges slightly up to 2 cm over 24 to 48 hours. In the middle, a small bump, vesicle, or bulla develops, flattens, and then may clear. The intermediate ring forms and becomes raised, pale, and swollen. The periphery slowly becomes purple and forms a concentric lesion, resembling a target. Some lesions are atypical targets with only 2 concentric rings.

The Koebner phenomenon may occur. This is where a lesion occurs along the line of trauma and it is typical of psoriasis and lichen planus.

Lesions appear first on the extensor surfaces of the periphery and extend centrally. The palms, neck and face are often involved but the soles and flexures of the extremities less often. There may be mucosal involvement in 70% of patients but it tends to be mild and limited to just one mucosal surface (for example mouth or vulva). Oral lesions are most common with lips, palate and gingiva affected. There may be red conjunctivae and tearing, but eye involvement tends to be mild. Genital involvement can produce painful hemorrhagic bullae and erosions.

No specific investigations are indicated. A punch biopsy may be required to confirm diagnosis.

In recurrent disease due to HSV, antiviral therapy is helpful. Symptomatic treatment may include analgesics, mouth wash and local skin care. Steroid creams may be used. If the mouth is very sore, attention may have to be given to hydration and nutrition. Lubricating drops for eyes may be required.

Secondary infection of lesions may occur. Serious complications are unusual in a patient with an intact immune system. A very sore mouth may lead to dehydration and poor nutrition.

Most disease subsides completely in 2 to 3 weeks without any complications.

Valerie Nozad, D.O.
Department of Dermatology
Philadelphia College of Osteopathic Medicine/Frankford Hospital
Philadelphia, Pennsylvannia.