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Erythema nodosum (EN)

Erythema nodosum (EN) is characterized by red or violet subcutaneous nodules that usually develop in a pretibial location. EN is presumed to represent a delayed hypersensitivity reaction to antigens associated with the various infectious agents, drugs, and other diseases. The pathogenesis is largely unclear. 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.

Differential diagnosis:

Cutaneous eruptions that can be confused with erythema nodosum include other forms of panniculitis, especially nodular vasculitis (erythema induratum), subcutaneous infections due to bacteria or fungi, superficial thrombophlebitis, and cutaneous vasculitides

Most common disorders:

  • Streptococcal infection (especially in children)
  • Other bacterial infections (eg, Yersinia, Salmonella, mycoplasma, chlamydia, leprosy, lymphogranuloma venereum)
  • Sarcoidosis
  • Inflammatory bowel disease
  • Fungal infections (eg, 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
  • Behçet disease
  • TB

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