Erythema nodosum

Background

Pathophysiology

• Delayed hypersensitivity reaction causing a septal panniculitis without vasculitis

Clinical Manifestations

• Erythematous, tender nodules on the shins

Differential Diagnosis

• Infections
  • Bacterial
    • Streptococcal infection (the most common infectious cause)
    • Tuberculosis
    • Leprosy
    • Yersinia, Salmonella, Campylobacter gastroenteritis
    • Mycoplasma pneumoniae
    • Tularemia
    • Leptospirosis
    • Brucellosis
    • Chlamydia trachomatis
    • Psittacosis
    • Lymphogranuloma venereum
    • Cat-scratch disease
  • Fungal
    • Coccidioidomycosis
    • Histoplasmosis
    • Blastomycosis
  • Viral
    • Infectious mononucleosis
    • Hepatitis B
    • Paravaccinia
• Drugs
  • Oral contraceptives
  • Penicillin
  • Sulfonamides
  • Bromides and iodides
  • TNF-α inhibitors (rare)
• Inflammatory bowel disease
  • Crohn disease (more often than ulcerative colitis)
  • Ulcerative colitis
• Malignancy
  • Lymphoma (Hodgkin, most often)
  • Leukemia (acute myelogenous, most often)
  • Internal carcinomas
• Miscellaneous
  • Sarcoidosis
  • Pregnancy
  • Whipple disease
  • Behçet disease
  • Sweet syndrome