Erythema Multiforme
Erythema multiforme is a recurring disorder characterized by patches of red, raised skin that often look like targets and usually are distributed symmetrically over the body.
Most cases are caused by a reaction to infection with the herpes simplex virus (see Section 17, Chapter 198). This viral infection is apparent as visible cold sores in about two thirds of people before the erythema multiforme appears. Doctors are not sure if other infectious diseases also cause erythema multiforme. Doctors are unsure exactly how herpes simplex causes this disorder, but a type of immune reaction is suspected.
Symptoms
Usually, erythema multiforme appears suddenly, with reddened patches erupting on the arms, legs, and face. Sometimes the rash is also present on the palms or soles. The red patches are distributed equally on both sides of the body; these red areas often develop red concentric rings with purple-gray centers (target or iris lesions) and small blisters. The reddened areas usually are symptomless, although they sometimes itch mildly. Painful blisters often form on the lips and lining of the mouth but do not involve the eyes.
Attacks of erythema multiforme may last 2 to 4 weeks. Some people have only one attack, but some have recurrences an average of 6 times a year for almost 10 years. Recurrences are more common in the spring and can probably be triggered by sunlight. The frequency of recurrence usually decreases with time.
Treatment
Erythema multiforme may resolve on its own. If itching is bothersome, standard treatments may be used. Corticosteroids given by mouth may be helpful. If painful mouth blisters make eating difficult, a topical anesthetic, such as lidocaine, may be applied. If oral intake is still poor, nutrition and fluids are given intravenously. People with frequent recurrences may benefit from an antiviral drug, such as acyclovir, given at the first sign of an outbreak.
| 
