What is the recommended diagnostic work‑up and treatment for erythema nodosum in an otherwise healthy adolescent or young adult?

Erythema Nodosum: Diagnostic Work-Up and Treatment

Diagnosis

Erythema nodosum is diagnosed clinically based on characteristic tender, raised, red or violet subcutaneous nodules measuring 1-5 cm in diameter, typically bilateral and symmetrical on the anterior tibial areas, without the need for routine biopsy. 1, 2

Clinical Features to Confirm

• Nodule characteristics: Sudden onset of tender, erythematous nodules on pretibial surfaces (anterior shins), bilateral and symmetrical distribution 2, 3
• Evolution pattern: Nodules change from bright red to livid/purplish, then yellow-green (bruise-like appearance) over days to weeks 4
• Key negative findings: No ulceration, no migration of individual lesions, heals without scarring 4, 3
• Systemic symptoms: Fever (60% of cases), malaise (67%), arthralgias (64%)—typically symmetrical, affecting distal lower extremities without effusions 2, 5

When to Perform Biopsy

Reserve skin biopsy only for atypical presentations where the diagnosis is uncertain—it is unnecessary for classic erythema nodosum. 1, 2, 3

Diagnostic Work-Up

Initial Laboratory Screening (All Patients)

• Complete blood count with differential (assess for eosinophilia, anemia) 6, 3
• Erythrocyte sedimentation rate and/or C-reactive protein (markers of inflammation) 6, 3
• Throat culture or rapid streptococcal antigen test plus anti-streptolysin O titer (streptococcal pharyngitis is the most common identifiable cause) 6, 3
• Chest radiograph (screen for sarcoidosis, tuberculosis, hilar adenopathy) 6, 3

Risk-Stratified Additional Testing

• If respiratory symptoms or endemic exposure: Serologic testing for coccidioidomycosis or histoplasmosis 2
• If high tuberculosis risk: Purified protein derivative (PPD) test or interferon-gamma release assay 6
• If gastrointestinal symptoms: Stool cultures, consider inflammatory bowel disease evaluation (IBD occurs in 4.2-7.5% of EN cases) 2, 7
• If recurrent oral/genital ulcers: Evaluate for Behçet's disease 2

Common Pitfall to Avoid

Do not perform extensive complement testing (C3, C4, C1q, C1-inhibitor) in typical erythema nodosum—EN does not cause complement abnormalities, and any isolated C4 elevation is unrelated and requires separate investigation. 2

Treatment Strategy

First-Line: Supportive Care and NSAIDs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the cornerstone of symptomatic treatment for pain and inflammation in erythema nodosum. 2, 7

• Bed rest and leg elevation to reduce discomfort 4, 3
• NSAIDs: Indomethacin, naproxen, or ibuprofen for analgesia and inflammation 4, 3
• Most cases are self-limited and resolve spontaneously within weeks with supportive care alone 4, 3

Treat the Underlying Cause

Management must address the identified trigger—EN usually resolves once the precipitating condition is treated. 2

• Streptococcal infection: Appropriate antibiotic therapy 6
• Sarcoidosis: Most cases (especially Löfgren's syndrome) resolve spontaneously; 85% with acute arthritis and EN have excellent prognosis 2
• Inflammatory bowel disease: Treat the underlying bowel inflammation 1, 2

Second-Line: Systemic Corticosteroids

Systemic corticosteroids are reserved for severe cases with significant inflammation or IBD-associated erythema nodosum, and should be used cautiously after excluding infectious causes—particularly tuberculosis. 1, 2, 7

• Corticosteroids are highly effective but carry risk of disseminating underlying infections 4, 5
• For IBD-associated EN, systemic steroids treat both the skin manifestations and underlying bowel disease 1, 7

Refractory or Recurrent Cases

For persistent or frequent relapses, escalate therapy in this order:

1. Colchicine: Particularly effective when EN is the dominant lesion or associated with Behçet's disease 2, 7
2. Azathioprine: For frequent relapses, especially in IBD-associated disease 1, 2, 7
3. TNF-α inhibitors (infliximab or adalimumab): For resistant cases associated with inflammatory bowel disease 1, 2, 7

Special Considerations

• Pregnancy-associated EN: Avoid NSAIDs in third trimester; supportive care is usually sufficient 8
• Drug-induced EN: Discontinue the offending agent (oral contraceptives, sulfonamides, halides) 4, 8

Key Clinical Pitfalls

• Do not start corticosteroids before excluding tuberculosis and other infections 2, 4
• Do not perform routine skin biopsy for typical presentations 1, 2
• Do not neglect to monitor for disease activity in associated conditions like IBD or sarcoidosis, as recurrent EN may indicate persistent underlying disease 2
• Do not attribute migratory nodules to EN—migration suggests alternative diagnoses such as gnathostomiasis or erythema nodosum migrans 2, 4