Erythema nodosum is an inflammatory disorder that produces tender red bumps (nodules) under the skin, most often over the shins but occasionally on the arms and other areas.
• Erythema nodosum usually is caused by another disease, drug sensitivity, or bacterial, fungal, or viral infection.
• Typical symptoms include fever, joint pain, and characteristic painful red bumps and bruises on the person's shins.
• The diagnosis is based on symptoms and supported by results of a chest x-ray, blood tests, and a biops.
• People stop taking suspected drugs; underlying infections are treated with antibiotics; and pain is relieved by bed rest, nonsteroidal anti-inflammatory drugs, and sometimes an injection with a corticosteroid.
Quite often, erythema nodosum is a symptom of some other disease or of sensitivity to a drug. Young adults, particularly women, are most prone to the disorder, which may recur for months or years. Bacterial, fungal, or viral infections may also cause erythema nodosum.
Streptococcal infection is one of the most common causes of erythema nodosum, particularly in children. Sarcoidosis, ulcerative colitis, and various drugs, such as sulfa antibiotics and oral contraceptives, are other common causes. Numerous other infections and several types of cancer are also thought to cause the eruption.
Erythema nodosum nodules usually appear on the shins and resemble raised bumps and bruises that gradually change from pink to bluish brown. Fever and joint pain are common. Lymph nodes in the chest occasionally become enlarged and are detected with a chest x-ray. The painful nodules are usually the telltale sign for the doctor. Evaluation includes chest x-ray, blood tests, and skin biopsy, in which a small piece of skin is surgically removed for examination under a microscope.
Treatment
Drugs that might be causing erythema nodosum are discontinued, and any underlying infections are treated. If the disorder is caused by a streptococcal infection, a person may have to take antibiotics, such as penicillin, or a cephalosporin.
The nodules may go away in 3 to 6 weeks without treatment. Bed rest and nonsteroidal anti-inflammatory drugs (NSAIDs) may help relieve the pain caused by the nodules. Individual nodules may also be treated by injecting them with a corticosteroid. When a person has many nodules, corticosteroid or potassium iodide tablets sometimes are prescribed to speed relief of pain.
Resource: Merck Manual Home Edition