Erythema Nodosum Overview



Definition: 

 • EN is an inflammatory condition characterized by tender, red nodules, typically located on the shins.



Nature:

 • It is a form of panniculitis, involving inflammation of the subcutaneous fat.



Significance: 

 • EN often serves as a marker for underlying systemic diseases.



Common Causes of EN:

 • Infectious Agents:

   - Streptococcal infections (most common)

   - Mycobacterium tuberculosis

   - Histoplasma capsulatum

   - Yersinia enterocolitica

   - Chlamydia trachomatis

   - Mycoplasma pneumoniae

   - Coccidioides immitis

   - Epstein-Barr virus

 • Systemic Diseases:

   - Sarcoidosis

   - Inflammatory bowel disease (Crohn’s disease, ulcerative colitis)

   - Behçet's disease

 • Medications:

   - Sulfonamides

   - Oral contraceptives

   - Penicillins

   - Omeprazole

   - Hepatitis B vaccine

 • Other Factors:

   - Pregnancy

   - Malignancies (e.g., non-Hodgkin lymphoma, pancreatic cancer)

   - Idiopathic (no identifiable cause in 30–50% of cases)



Clinical Presentation of Erythema Nodosum (EN):

 • EN typically presents as the sudden onset of painful, erythematous, warm nodules or plaques, most commonly located on the anterior aspects of the lower legs (shins).

 • The lesions are usually bilateral but may be asymmetric, and they range in size from 1 to 5 cm. Patients may also report systemic symptoms such as fever, malaise, arthralgia (especially in the ankles and knees), and fatigue.

 • The nodules evolve over several days, starting as bright red and becoming violaceous, then fading to a bruise-like appearance before resolving spontaneously over 2 to 8 weeks without ulceration or scarring.



Diagnostic Approach:

Clinical Evaluation:

 • Detailed patient history and physical examination.

Laboratory Tests:

 • Complete blood count (CBC)

 • Erythrocyte sedimentation rate (ESR)

 • C-reactive protein (CRP)

 • Antistreptolysin O (ASO) titer

 • Throat culture

 • Tuberculin skin test

 • Chest radiograph (especially to assess for sarcoidosis)

Histopathology:

 • Skin biopsy may reveal septal panniculitis without vasculitis



Management Strategies:

Address Underlying Cause:

 • Treat infections, manage systemic diseases, discontinue offending drugs.

Symptomatic Treatment:

 • Nonsteroidal anti-inflammatory drugs (NSAIDs) for pain and inflammation.

 • Bed rest and leg elevation.

 • Compression therapy.

 • Potassium iodide for persistent cases.

 • Corticosteroids or colchicine in refractory cases.



Prognosis:

 • EN is generally self-limiting, resolving within 3–6 weeks.

 • Recurrence is possible, especially if the underlying cause persists.



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