Erythema Nodosum

Medical Author: William C. Shiel Jr., MD, FACP, FACR
Medical Editor: Dennis Lee, MD

• What is erythema nodosum?
• What causes erythema nodosum?
• How is erythema nodosum diagnosed?
• How is erythema nodosum treated?

What is erythema nodosum?

Erythema nodosum is a type of skin inflammation that is located in a certain portion of the fatty layer of skin. Erythema nodosum (also called EN) results in reddish, painful, tender lumps most commonly located in the front of the legs below the knees. The tender lumps, or nodules, of erythema nodosum range in size from 1 to 5 centimeters. The nodular swelling is caused by a special pattern of inflammation in the fatty layer of skin.

Erythema nodosum can be self-limited and resolve on its own in three to six weeks. Upon resolution, it may leave only a temporary bruised appearance or leave a chronic indentation in the skin where the fatty layer has been injured.

There are several scenarios for the outcome of erythema nodosum. Typically, these areas of nodular tenderness range in size from about a dime to a quarter and they may be tender and inflamed off and on for a period of weeks. They usually then resolve spontaneously, each one of the little areas of inflammation shrinking down and then becoming flat rather than raised and inflamed. They leave a bruised appearance. Then, they resolve spontaneously completely. Other lesions can sometimes pop up elsewhere. This may occur for periods of weeks to months and then eventually goes away. However, chronic erythema nodosum that may last for years is another pattern. Chronic erythema nodosum, with intermittent recurrences, can occur with or without an underlying disease present.

What causes erythema nodosum?

Erythema nodosum may occur as an isolated condition or in association with other conditions. Conditions that are associated with erythema nodosum include medications (sulfa-related drugs, birth control pills, estrogens), strep throat, Cat scratch disease, fungal diseases, infectious mononucleosis, sarcoidosis, Behcet's disease, inflammatory bowel diseases (Crohn's disease and ulcerative colitis), and normal pregnancy.

How is erythema nodosum diagnosed?

Usually, erythema nodosum is a straightforward, simple diagnosis for a doctor to make simply by examining a patient and noting the typical firm area of raised tenderness that is red along with areas which have had lesions resolved, which might show a bruised-like appearance. It is not a difficult diagnosis for an experienced doctor. It does not typically require other investigative tests.

Sometimes a biopsy is done for confirmation, for example, if a patient presented with an isolated, singular area and a doctor was unable to make a diagnosis based on its appearance. The biopsy of the deeper layers of tissue of skin can prove that it is erythema nodosum. Those layers would show the specific fatty layers of inflammation.

How is erythema nodosum treated?

Erythema nodosum is initially managed by identifying and treating any underlying condition present. Simultaneously, treatment is directed toward the inflamed skin from the erythema nodosum.

Treatments for erythema nodosum include antiinflammatory drugs, and cortisone by mouth or injection. Colchicine is sometime used effectively to reduce inflammation. Treatment must be customized for the particular patient and conditions present. It is important to note that erythema nodosum, while annoying and often painful, does not threaten internal organs and the long-term outlook is generally very good.

References: Clinical Primer of Rheumatology, Lippincott Williams & Wilkens, edited by William Koopman, et al., 2003.

Kelley's Textbook of Rheumatology, W B Saunders Co, edited by Shaun Ruddy, et al., 2000.

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