Definition

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

Causes

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.

Symptoms

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

Exams and Tests

Your health care provider can diagnose this condition by looking at your skin. Tests that may be done include:

• Punch biopsy of a nodule
• Throat culture to check for a strep infection
• Chest x-ray to check for sarcoidosis or tuberculosis
• Blood tests to look for infections or other disorders

Treatment

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.

Outlook (Prognosis)

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

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

When to Contact a Medical Professional

Contact your provider if you develop symptoms of erythema nodosum.

References

James WD, Elston DM, Treat JR, Rosenbach MA. Diseases of the subcutaneous fat. In: James WD, Elston DM, Treat JR, Rosenbach MA, Neuhaus IM, eds. Andrews' Diseases of the Skin: Clinical Dermatology. 13th ed. Philadelphia, PA: Elsevier; 2020:chap 23.

Korsten P, Sweiss NJ, Baughman RP. Sarcoidosis. In: Firestein GS, Budd RC, Gabriel SE, Koretzky GA, McInnes IB, O'Dell JR, eds. Firestein & Kelley's Textbook of Rheumatology. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 124.

Moon M, Guerrero AM, Li X, Koch E, Gehris RP. Dermatology. In: Zitelli BJ, McIntire SC, Nowalk AJ, Garrison J, eds. Zitelli and Davis' Atlas of Pediatric Diagnosis. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 8.

Shields BE, Forrestel A, Rosenbach M. Erythema nodosum. In: Lebwohl MG, Heymann WR, Coulson IH, Murrell DF, eds. Treatment of Skin Disease: Comprehensive Therapeutic Strategies. 6th ed. Philadelphia, PA: Elsevier; 2022:chap 76.

Zamore R, Bewtra M, Ogdie A. Inflammatory bowel disease-associated arthritis and other enteropathic arthropathies. In: Firestein GS, Budd RC, Gabriel SE, Koretzky GA, McInnes IB, O'Dell JR, eds. Firestein & Kelley's Textbook of Rheumatology. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 83.