Erythema nodosum (EN) is an inflammatory condition characterized by inflammation of subcutaneous fat tissue, resulting in painful red/blue lumps or nodules that are usually seen symmetrically on both shins, on the thighs, arms, and elsewhere.

The first signs of erythema nodosum are often flu-like symptoms such as a fever, cough, malaise, and aching joints.

[19] A useful mnemonic for causes is SORE SHINS (Streptococci, OCP, Rickettsia, Eponymous (Behçet), Sulfonamides, Hansen's Disease (Leprosy), IBD, NHL, Sarcoidosis.

Although circulating immune complexes have been demonstrated in patients with inflammatory bowel disease, they have not been found in idiopathic or uncomplicated cases.

[4] Microscopic examination usually reveals a neutrophilic infiltrate surrounding capillaries that results in septal thickening, with fibrotic changes in the fat around blood vessels.

A characteristic microscopic finding is radial granulomas, well-defined nodular aggregates of histiocytes surrounding a stellate cleft.

This may include a full blood count (FBC), erythrocyte sedimentation rate (ESR), antistreptolysin-O (ASO) titer and throat culture, urinalysis, intradermal tuberculin test, and a chest x-ray.

Symptoms can be treated with bed rest, leg elevation, compressive bandages, wet dressings, and nonsteroidal anti-inflammatory agents (NSAIDs).