Erythema multiforme is usually caused by a reaction to an infection, usually herpes simplex virus.
Typical symptoms include red patches with purple-gray centers (target lesions) that suddenly appear on the palms and soles, arms and legs, and face and may later spread to the body.
Many people have mouth sores.
The diagnosis is by a doctor's recognition of the target lesions.
This disorder resolves without treatment, but symptoms can be treated with corticosteroids, antihistamines, and anesthetics applied to the skin.
If people have frequent attacks and the doctor thinks herpes simplex virus is the cause, an antiviral drug may help prevent recurrences.
Most cases are caused by a reaction to infection with the herpes simplex virus. Some people with erythema multiforme develop herpesvirus cold sores on their lips several days before an attack of erythema multiforme.
Less often, cases are caused by bacterial infections (such as mycoplasma), drugs, vaccines, infections with other viruses (especially hepatitis C), and certain noninfectious diseases that affect the immune system, such as systemic lupus erythematosus.
Doctors are unsure exactly how erythema multiforme happens, but a type of immune reaction is suspected. Some cases of erythema multiforme do not have a clear cause.
Attacks of erythema multiforme may last 2 to 4 weeks. Some people have only one attack, but some have multiple recurrences. Recurrences are common, especially when the cause is herpes simplex virus. The frequency of recurrence usually decreases with time.
Usually, erythema multiforme appears suddenly, with reddened bumps erupting on the arms, legs, and face and then enlarging into circles. Often the rash is also present on the palms and soles. The red areas are distributed equally on both sides of the body. They often develop pale rings inside the patches and purple centers (called “target” or “iris” lesions) and small blisters. The red patches may cause no symptoms, but they sometimes itch or burn mildly. Painful blisters or sores often form on the lips and lining of the mouth and rarely in the eyes.
Doctors diagnose erythema multiforme by its characteristic appearance. However, Stevens-Johnson syndrome may at first look very similar to erythema multiforme, so doctors monitor the person carefully until the diagnosis is clear.
Erythema multiforme resolves on its own, so treatment is usually not necessary. However, treatment of any underlying infection is helpful. If itching is bothersome, standard itching treatments, such as anesthetics and corticosteroids applied to the skin and antihistamines taken by mouth, may be helpful.
If painful mouth blisters make eating difficult, an anesthetic (numbing) liquid, such as lidocaine, may be applied to the inside of the mouth. If people are still not able to eat or drink well, nutrition and fluids are given intravenously.
People with frequent recurrences, especially when the doctor suspects herpesvirus may be the cause, may benefit from an antiviral drug (such as acyclovir, famciclovir, or valacyclovir) given at the first sign of an outbreak.