Erythema multiforme is a skin condition of unknown cause; it is a type of erythema possibly mediated by deposition of immune complexes in the superficial microvasculature of the skin and oral mucous membrane that usually follows an infection or drug exposure. It is an uncommon disorder, with peak incidence in the second and third decades of life. The disorder has various forms or presentations, which its name reflects. Target lesions are a typical manifestation. Two types, one mild to moderate and one severe, are recognized.
Signs and symptoms
The condition varies from a mild, self-limited rash to a severe, life-threatening form known as erythema multiforme major that also involves mucous membranes. Consensus classification:
Erythema multiforme minor—typical targets or raised, edematous papules distributed
Erythema multiforme major—typical targets or raised, edematous papules distributed acrally with involvement of one or more mucous membranes; epidermal detachment involves less than 10% of total body surface area
Stevens–Johnson syndrome and toxic epidermal necrolysis used to be considered part of the erythema multiforme spectrum, that is no longer the case. The mild form usually presents with mildly itchy, pink-red blotches, symmetrically arranged and starting on the extremities. It often takes on the classical "target lesion" appearance, with a pink-red ring around a pale center. Resolution within 7–10 days is the norm. Individuals with persistent erythema multiforme will often have a lesion form at an injury site, e.g. a minor scratch or abrasion, within a week. Irritation or even pressure from clothing will cause the erythema sore to continue to expand along its margins for weeks or months, long after the original sore at the center heals.
Causes
Many suspected aetiologic factors have been reported to cause EM.
EM minor is regarded as being triggered by HSV in almost all cases. A herpetic aetiology also accounts for 55% of cases of EM major. Among the other infections, Mycoplasma'' infection appears to be a common cause. Herpes simplex virus suppression and even prophylaxis has been shown to prevent recurrent erythema multiforme eruption.
Treatment
Erythema multiforme is frequently self-limiting and requires no treatment. The appropriateness of glucocorticoid therapy can be uncertain, because it is difficult to determine if the course will be a resolving one.
