Erythema nodosum is characterised by red nodules that are tender and warm.^[1] Nodules occur under the skin, classically in front of the shins. Nodules may occur anywhere there is fat under the skin, including the thighs, arms, trunk, face, and neck.^[1]

Erythema nodosum may occur concurrently with fever, malaise, and joint pain and inflammation.^[1] Nodules vary from 1–10 cm in diameter, and may coalesce to form large areas of hardened skin.^[2]

As the nodules age, they become bluish purple, brownish, yellowish, and finally green, similar to the color changes that occur in a resolving bruise. The nodules usually subside over a period of 2–6 weeks without ulceration or scarring.^[3]

Erythema nodosum is self-limiting. A recurring form does exist, and in children it is attributed to repeated infections with streptococcus.^[10] Treatment should focus on the underlying cause. Symptoms can be treated with bedrest, leg elevation, compressive bandages, wet dressings, and nonsteroidal anti-inflammatory agents (NSAIDs).^[3] NSAIDs are usually more effective at the onset of EN versus with chronic disease.

Potassium iodide can be used for persistent lesions whose cause remains unknown. Corticosteroids and colchicine can be used in severe refractory cases.^[15][16] Thalidomide has been used successfully in the treatment of Erythema nodosum leprosum,^[17] and it was approved by the U.S. FDA for this use in July 1998.^[18]