Erythema multiforme is a cutaneous reaction pattern characterized by macules, papules, and plaques with at least some of the lesions showing the characteristic "iris" or "target" lesion morphology. The "iris" lesion is an erythematous plaque with a slightly depressed, more purple center which can be bullous.
Lesions characteristically involve the palms and soles as well as the rest of the body surface.
Erythema multiforme is usually idiopathic but the most common known cause is Herpes simplex, with the erythema multiforme forming 1-3 weeks after development of a typical Herpes simplex lesion.
When there is extensive mucous membrane involvement with or without other skin involvement, the eruption is termed the Stevens-Johnson syndrome.
The most severe erythema multiforme is known as toxic epidermal necrolysis.
- Severe erythema multiforme of the toxic epidermal necrolysis variant requires management by skilled nurses in the burn unit of a hospital. Skin, and therefore systemic infection, is the greatest risk to the patient.
- Mild to moderate erythema multiforme requires symptomatic treatment only. There is no specific systemic therapy to treat a well developed erythema multiforme.
- High dose systemic prednisone can be considered but there are not good trials that would suggest that the benefits of high dose prednisone exceed the risk.
- Recurrent erythema multiforme warrants treatment with acyclovir to control the occurrence of recurrent Herpes simplex.
- Long term treatment with low dose acyclovir is highly effective at blocking recurrent erythema multiforme secondary to Herpes simplex.
- Case reports show benefits from Dapsone, Azathioprine and Thalidomide.