After appropriate workup, the patient was started on supersaturated potassium iodide.

ERYTHEMA NODOSUM

Erythema nodosum (EN) is the most common panniculitis and may develop in response to a wide variety of antigens. In this unique reaction pattern, exquisitely tender nodules develop on the shins.

• Most common panniculitis
• Tender, erythematous, subcutaneous nodules with septal panniculitis.
• Usually symmetric and favors lower legs
• +/- systemic symptoms
• Considered a delayed hypersensitivity, possibly Th1 mediated
• Usually self-limited and resolves in 2-6 weeks

Clinical

The typical patient experiences the acute onset of multiple deep-seated, red nodules on both shins. Pain is often severe. Some patients limp or can't even walk. It usually runs its course over 3-6 weeks. Lesions on the thighs or arms are less common. There is a a chronic variant also known as Villanova disease that may present as a solitary, slowly enlarging red plaque on the lower leg.

Possible Causes

The most important first step is to determine, if possible, the cause. Any of a variety of antigen exposures may be implicated.

• Infections: Group A beta-haemolytic Streptococcus, Yersinia, Salmonella, Campylobacter, Mycobacterium tuberculosis, Epstein–Barr virus, Parvovirus B19, Cytomegalovirus, Dermatophytes, Hepatitis, Blastomycosis, Histoplasmosis, Coccidioidomycosis, Sporothrix, non-specific URI, chlamydia

• Drugs: Oral contraceptives, Macrolides, Cephalosporin, Penicillin, BRAF inhibitor therapy

• Inflammatory diseases: Behçet's disease, Sarcoidosis, Ulcerative colitis, Crohn's disease

• Others: Hodgkin's disease, pregnancy, radiation of a neoplasm.

• Idiopathic

Diagnosis and Workup

In most cases, a skin biopsy is not needed for diagnosis but may be helpful in atypical cases. A high fever, respiratory symptoms and/or an abnormal chest X-ray may signal a causative lung process, e.g. pneumonia. Workup may include:

• CBC (infection)
• u.a.
• ASO
• Pregnancy test
• Throat and urine cultures (Blood if indicated)
• PPD or interferon gold, CXR (for TB and sarcoidosis)
• ACE level (for sarcoidosis)
• liver enzymes
• stool culture if diarrhea is present
• Intradermal or serologic tests for deep fungi (if indicated)

RegionalDerm

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