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.
- The tender lumps, or nodules, of erythema nodosum range in size from one to five centimeters. Inflammation in the fatty layer of skin causes the nodular swelling.
- 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 was injured.
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, and estrogens),
- strep throat,
- Cat scratch disease,
- fungal diseases,
- infectious mononucleosis,
- Behçet's disease,
- inflammatory bowel diseases (Crohn's disease and ulcerative colitis), and
- normal pregnancy.
What are the signs and symptoms of erythema nodosum?
Characteristic features of erythema nodosum include barely raised, tender, reddish nodules, most commonly below the knees in the front of the legs. They are typically painful and can slowly come and go.
There are several scenarios for the outcome of erythema nodosum. Typically, these nodular areas are 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 completely on their own. Other lesions can sometimes pop up elsewhere. This may occur for periods of weeks to months, and then they eventually disappear. 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.
How do health care professionals diagnose erythema nodosum?
Usually, erythema nodosum is a straightforward, simple diagnosis for a doctor to make 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 does not typically require other investigative tests.
Sometimes doctors perform a biopsy for confirmation. For example, if a patient presents with an isolated, nodule and a doctor is 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.
Can erythema nodosum be confused with other conditions?
The nodules of erythema nodosum are sometimes confused with insect bites. Sometimes the inflammation of erythema nodosum is more widespread and can mimic skin infection (cellulitis).
Rosacea, Acne, Shingles: Common Adult Skin Diseases
Diagnosis of Erythema Nodosum
A skin biopsy is the removal of a piece of skin for the purpose of further examination in the laboratory using a microscope. Skin biopsies are performed to diagnose a number of conditions. Biopsies are not meant to actually treat a skin condition.
What are treatment options for erythema nodosum?
Doctors manage erythema nodosum by identifying and treating any underlying condition present. Simultaneously, health care professionals direct treatment toward the inflamed skin from the erythema nodosum.
Treatments for erythema nodosum include anti-inflammatory drugs and corticosteroids by mouth or local injection. Physicians sometimes administer colchicine to reduce inflammation. Treatment must be customized for the particular patient and conditions present, such as the existence of any associated diseases. 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.
Medically Reviewed on 5/15/2018
Koopman, William, et al., eds. Clinical Primer of Rheumatology. Philadelphia, PA: Lippincott Williams & Wilkins, 2003.
Ruddy, Shaun, et al. Kelley's Textbook of Rheumatology. 6th ed. Philadelphia, PA: W.B. Saunders, 2001.