Erythema nodosum is a type of inflammation that results in painful lumps (nodules) forming on the extremities, usually the lower legs.
The red lumps can vary in size and number and evolve into purple lesions that resemble bruises.
People with erythema nodosum often complain of a previous respiratory infection or fever and general sense of fatigue. About half of the individuals affected develop joint pain, usually in the knees. The exact cause of erythema nodosum is unknown, but it has been associated with pregnancy, certain infections (including streptococcus, mononucleosis, histoplasmosis, and hepatitis B), certain medications (including oral contraceptives, penicillin, sulfonamides, and some anticonvulsants), leukemia, sarcoidosis, and ulcerative colitis.
Treatment is directed at controlling the underlying condition or eliminating the suspected offending medication.
Symptoms usually resolve by 6 weeks but may recur.