Erythema Nodosum



  • Erythema nodosum (EN) is characterized by multiple symmetric, nonulcerative tender nodules on the extensor surface of the lower extremities
  • Typically in young adults
  • Peak incidence in third decade
  • More common in women (4:1)
  • Nodules are round with poorly demarcated edges and vary in size from 1–10 cm
  • Skin lesions are initially red, become progressively ecchymotic appearing as they resolve over 3–6 wk
  • Lesions are caused by inflammation of the septa between SC fat nodules (septal panniculitis)
  • Spontaneous regression of lesions within 3–6 wk
  • Major disease variants include:
    • EN migrans (usually mild unilateral disease with little or no systemic symptoms)
    • Chronic EN (lesions spread via extension, and associated systemic symptoms tend to be milder)


  • Immune-mediated response
  • 30–50% of the time etiology is idiopathic
  • Often a marker for underlying disease; specific etiologies include:
    • Drug reactions:
      • Oral contraceptives
      • Sulfonamides
      • Penicillins
    • Infections including:
      • Streptococcal pharyngitis
      • Mycobacterium tuberculosis (TB)
      • Atypical mycobacteria
      • Coccidioidomycosis
      • Hepatitis
      • Herpes simplex
      • Infectious mononucleosis
      • Syphilis
      • Chlamydia
      • Rickettsia
      • Salmonella
      • Campylobacter
      • Yersinia
      • Parasites
      • Leprosy
    • Systemic diseases:
      • Sarcoidosis
      • Inflammatory bowel disease
      • Behçet disease
      • Connective tissue disorders
    • Malignancies such as lymphoma and leukemia
    • Catscratch disease
    • HIV infection
    • Rarely can be caused by vaccines for hepatitis and TB (BCG)
    • Pregnancy

Pediatric Considerations
Typically, EN begins 2–3 wk after onset of streptococcal pharyngitis

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