Erythema Nodosum

By Wingfield E. Rehmus, MD, MPH, Clinical Assistant Professor, University of British Columbia

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Hypersensitivity and Inflammatory Disorders
Introduction to Hypersensitivity and Inflammatory Disorders
Acute Febrile Neutrophilic Dermatosis
Drug Eruptions and Reactions
Erythema Multiforme
Panniculitis
Erythema Nodosum
Granuloma Annulare
Pyoderma Gangrenosum
Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)

Erythema nodosum (EN) is a specific form of panniculitis (see Panniculitis) characterized by tender, red or violet, palpable, subcutaneous nodules on the shins and occasionally other locations. It often occurs with an underlying systemic disease, notably streptococcal infections, sarcoidosis, and inflammatory bowel disease. Diagnosis is by clinical evaluation and sometimes biopsy. Treatment depends on the cause.

Etiology

EN primarily affects people in their 20s and 30s but can occur at any age; women are more often affected. Etiology is unknown, but an immunologic reaction is suspected because EN is frequently accompanied by other disorders. The most common disorders are

Streptococcal infection (especially in children)
Sarcoidosis
Inflammatory bowel disease

Other possible triggering disorders include

Other bacterial infections (eg, Yersinia,Salmonella, mycoplasma, chlamydia, leprosy, lymphogranuloma venereum)
Fungal infections (eg, kerion, coccidioidomycosis, blastomycosis, histoplasmosis)
Rickettsial infections
Viral infections (eg, Epstein-Barr, hepatitis B)
Use of drugs (eg, sulfonamides, iodides, bromides, oral contraceptives)
Hematologic and solid cancers
Pregnancy
Behçet disease
TB

Up to one third of cases of EN are idiopathic.

Erythema induratum, a similar disorder, manifests with lesions on the calves and classically affects patients with TB.

Symptoms and Signs

EN is a subset of panniculitis that manifests as erythematous, tender nodules or plaques, primarily in the pretibial region, often preceded or accompanied by fever, malaise, and arthralgia. Lesions may be detected more easily by palpation than inspection and can evolve into bruiselike areas over weeks.

Diagnosis

Clinical evaluation
Excisional biopsy

Diagnosis is usually by clinical appearance and can be confirmed by excisional biopsy of a nodule when necessary. A diagnosis of EN should prompt evaluation for causes. Evaluation might include biopsy, skin testing (PPD or anergy panel), antinuclear antibodies, CBC, chest x-ray, and serial antistreptolysin O titers or a pharyngeal culture. ESR is often high.

Treatment

Supportive care
Anti-inflammatory drugs (rarely corticosteroids)

EN almost always resolves spontaneously. Treatment includes bed rest, elevation, cool compresses, and NSAIDs. K iodide 300 to 500 mg po tid can be given to decrease inflammation. Systemic corticosteroids are effective but should be used only as a last resort because they can worsen an occult infection. If an underlying disorder is identified, it should be treated.

Key Points

The most common causes of EN are streptococcal infections (particularly in children), sarcoidosis, and inflammatory bowel disease.
Diagnose EN primarily by clinical appearance but, when necessary, excise a nodule for biopsy confirmation.
Treat EN supportively and use NSAIDs or K iodide as needed until the disorder resolves spontaneously.