Erythema nodosum: a sign of systemic disease.

Erythema nodosum, a painful disorder of the subcutaneous fat, is the most common type of panniculitis. Generally, it is idiopathic, although the most common identifiable cause is streptococcal pharyngitis. Erythema nodosum may be the first sign of a systemic disease such as tuberculosis, bacterial or deep fungal infection, sarcoidosis, inflammatory bowel disease, or cancer. Certain drugs, including oral contraceptives and some antibiotics, also may be etiologic. The hallmark of erythema nodosum is tender, erythematous, subcutaneous nodules that typically are located symmetrically on the anterior surface of the lower extremities. Erythema nodosum does not ulcerate and usually resolves without atrophy or scarring. Most direct and indirect evidence supports the involvement of a type IV delayed hypersensitivity response to numerous antigens. A deep incisional or excisional biopsy specimen should be obtained for adequate visualization. Erythema nodosum represents an inflammatory process involving the septa between subcutaneous fat lobules, with an absence of vasculitis and the presence of radial granulomas. Diagnostic evaluation after comprehensive history and physical examination includes complete blood count with differential; erythrocyte sedimentation rate, C-reactive protein level, or both; testing for streptococcal infection (i.e., throat culture, rapid antigen test, antistreptoly-sin-O titer, and polymerase chain reaction assay); and biopsy. Patients should be stratified by risk for tuberculosis. Further evaluation (e.g., purified protein derivative test, chest radiography, stool cultures) varies based on the individual. Erythema nodosum tends to be self-limited. Any underlying disorders should be treated and supportive care provided. Pain can be managed with nonsteroidal anti-inflammatory drugs.