Erythema nodosum
Erythema nodosum is a delayed hypersensitivity panniculitis presenting as symmetric, tender, erythematous subcutaneous nodules on the anterior shins, most commonly following streptococcal pharyngitis but also linked to sarcoidosis, inflammatory bowel disease, Coccidioides, Yersinia, pregnancy, and drugs such as oral contraceptives. Diagnosis is clinical, and management is directed at the underlying cause with NSAIDs, bed rest, and cool compresses for symptom control.
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What this article covers
- Overview
Definition: erythema nodosum (EN) is a delayed hypersensitivity reaction causing panniculitis, inflammation of the subcutaneous fat, that presents as tender, erythematous nodules.
- Epidemiology
Sex distribution: more common in women, and often presents with associated joint pain.
- Risk factors
Recent streptococcal infection: the leading identifiable antecedent.
- Pathophysiology
Delayed (type IV) hypersensitivity reaction: immune complexes and a delayed cell-mediated response localize to the subcutaneous fat rather than the epidermis.
- Clinical features
Diagnostic nodules: tender, erythematous, subcutaneous nodules about the size of a quarter, most commonly on the anterior lower legs, bilateral and symmetric.
- Differential diagnosis
Cellulitis: unilateral, warm, poorly demarcated erythema without the bilateral symmetric nodular pattern of EN, and typically progresses over days rather than presenting as fixed nodules.
- Diagnosis
Clinical diagnosis from the classic presentation: bilateral, tender, erythematous nodules confined to the anterior shins in a patient with a compatible history establishes the diagnosis; biopsy is…
- Management
First, identify and treat the underlying cause: address the trigger directly (treat streptococcal pharyngitis, discontinue an implicated drug, or manage sarcoidosis or inflammatory bowel disease)…
- Complications
Persistent or recurrent nodules: can occur if the underlying trigger (for example ongoing oral contraceptive use or unrecognized inflammatory bowel disease) is not addressed.
- Prognosis
Favorable in most cases: EN is typically self-limited and resolves without scarring or ulceration once the trigger resolves or is treated.
- Prevention
Address modifiable triggers: discontinuing an implicated oral contraceptive or sulfonamide drug reduces the chance of recurrence.
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