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Erythema Nodosum

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Medical Author:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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Medical Editor:

Dennis Lee, MD

Dennis Lee, MD

Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.

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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.