Erythema nodosum is an inflammatory disorder. It involves tender, red bumps (nodules) under the skin.

In about half of cases, the exact cause of erythema nodosum is unknown. The remaining cases are associated with an infection or other systemic disorder.

Some of the more common infections associated with the disorder are:

• Streptococcus (most common)
• Cat scratch disease
• Chlamydia
• Coccidioidomycosis
• Hepatitis B
• Histoplasmosis
• Leptospirosis
• Mononucleosis (EBV)
• Mycobacteria
• Mycoplasma
• Psittacosis
• Syphilis
• Tuberculosis
• Tularemia
• Yersinia

Erythema nodosum may occur with sensitivity to certain medicines, including:

• Antibiotics, including amoxicillin and other penicillins
• Sulfonamides
• Sulfones
• Birth control pills
• Progestin

Sometimes, erythema nodosum may occur during pregnancy.

Other disorders linked to this condition include leukemia, lymphoma, sarcoidosis, rheumatic fever, Behcet disease, and ulcerative colitis.

The condition is more common in women than it is in men.

Erythema nodosum is most common on the front of the shins. It may also occur on other areas of the body such as buttocks, calves, ankles, thighs, and arms.

The lesions begin as flat, firm, hot, red, painful lumps that are about 1 inch (2.5 centimeters) across. Within a few days, they may become purplish in color. Over several weeks, the lumps fade to a brownish, flat patch.

Other symptoms may include:

• Fever
• General ill feeling (malaise)
• Joint aches
• Skin redness, inflammation, or irritation
• Swelling of the leg or other affected area

The underlying infection, drug, or disease should be identified and treated.

Treatment may include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs).
• Stronger anti-inflammatory medicines called corticosteroids, taken by mouth or given as a shot.
• Potassium iodide (SSKI) solution, most often given as drops added to orange juice.
• Other oral medicines that work on the body's immune system.
• Pain medicines (analgesics).
• Rest.
• Raising the sore area (elevation).
• Hot or cold compresses to help reduce discomfort.

Erythema nodosum is uncomfortable, but not dangerous in most cases.

Symptoms most often go away within about 6 weeks, but may return.

Contact your provider if you develop symptoms of erythema nodosum.

Published Date : August 14, 2021
Published By : Elika Hoss, MD, Senior Associate Consultant, Mayo Clinic, Scottsdale, AZ. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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