Dermatology

Erythema nodosum

Erythema nodosum is a tender septal panniculitis and reaction pattern, usually presenting with bilateral shin nodules that fade like bruises; the key task is identifying an infectious, inflammatory, drug-related, pregnancy-related or other trigger.

Definition

Erythema nodosum is an inflammatory panniculitis, usually septal and without vasculitis, that presents as tender subcutaneous nodules and reflects a reaction to an underlying trigger or may be idiopathic.

First principles

A reaction pattern in subcutaneous fat

Erythema nodosum is inflammation of the subcutaneous fat, classically a septal panniculitis without vasculitis. It is best understood as a skin manifestation of an immune response to a trigger rather than a single disease with one cause. The diagnosis is clinical in a typical presentation, but atypical lesions need reconsideration or biopsy.

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