More about erythema multiformeDear Dr. Roach:My sister broke out in a full-body rash of red, itchy blotches, and her doctor told her it was erythema multiforme. It is rare, and he sees only a few cases per year. Could you elaborate more on it — causes, treatment, etc.? — A.M.Dr. Roach: Erythema multiforme is a skin condition with a characteristic rash — it looks like a target. There is a red ring with a dot in the center, which makes it different from the bull’s-eye rash that occurs in a minority of cases of Lyme disease — that ring has central clearing. The “multiforme” reminds us that the rash might appear differently in one person than another, or in the same person in different areas or over time. EM is immune-mediated, stemming from an immune-system misfire, and is a clue to the doctor that there is something else going on. This usually is an infection — especially a herpes virus infection. There is a long list of other infections, such as mycoplasma pneumonia, viral hepatitis and salmonella, that are associated with EM. Sarcoidosis, a poorly understood, multisystem illness, is classically linked with EM, and about 10 percent of cases are drug-related, especially to anti-inflammatory drugs. In most cases, the rash disappears within two weeks, though a few people get recurrent EM. Treatment of EM is for the underlying condition, if it’s known. Mild cases are treated with topical steroids and topical or oral antihistamines. Severe cases often are treated with oral steroids, despite a lack of definitive proof that they help. Recurrent cases require more expertise, possibly the care of a skin specialist.