Erythema nodosum is an immunemediated disorder resulting in red tender pretibial subcutaneous nodules.
1–5 per 100,000 per year.
Peak incidence 15–40 years.
F > M
Streptococcal pharyngitis is the most common associated condition.
Many cases are idiopathic but this is a diagnosis of exclusion.
Drugs: Penicillin, oral contraceptive pill. Pregnancy.
Conditions with hilar lymphadenopathy: Sarcoidosis, tuberculosis, coccidioidomycosis, histoplasmosis, Hodgkin’s lymphoma and Chlamydophila pneumoniae.
Gastrointestinal disorders: Inflammatory bowel disease, Behc¸et’sˆ syndrome and bacterial gastroenteri-tides.
Painful bluishred nodules up to 5 cm in diameter appear in crops over 2 weeks on the anterior surface of both lower legs. They slowly fade leaving bruising and scarring of skin. Malaise, fever and arthralgia may accompany the rash.
Symptomatic treatment and management of any underlying cause is essential. Recovery may take weeks, and there may be recurrence.