Erythema multiforme is an erythematous rash caused by a hypersensitivity reaction.
The most common causes are viral infections and medications. It is also notably associated with the herpes simplex virus (causing coldsores) and mycoplasma pneumonia.
Erythema multiforme produces a widespread, itchy, erythematous rash. It produces characteristic “target lesions”. Target lesions are red rings within larger red rings, with the darkest red at the centre, similar to a bulls-eye target. It does not usually affect the mucous membranes but can cause a sore mouth (stomatitis).
The symptoms come on abruptly over a few days. It may be associated with other symptoms of mild fever, stomatitis, muscle and joint aches, headaches and general flu-like symptoms.
The diagnosis is made clinically based on the appearance of the rash.
It is important to identify the underlying cause. Where there is a clear underlying cause, for example a recent coldsore or treatment with penicillin, it may be managed supportively. Where there is no clear underlying cause it may be worth investigating further, for example doing a chest xray to look for mycoplasma pneumonia.
Most of the time erythema multiforme is mild and resolves spontaneously within one to four weeks without any treatment or lasting effects. Cases may be recurrent, particularly associated with recurrent coldsores.
Severe cases may require admission to hospital, particularly where it affects the oral mucosa. Treatments used in severe cases include IV fluids, analgesia and steroids (systemic or topical). The use of systemic steroids is controversial. Antibiotics or antivirals may be used where infection is present.
Last updated January 2020