Erythema Nodosum



Delayed-type hypersensitivity reaction leading to inflammation of the subcutaneous fat (panniculitis) and characterized by red, tender nodules on the shins


  • Girls slightly more frequently affected than boys
  • Incidence peaks in adolescence and is rare <2 years of age.


Delayed hypersensitivity immune response to various antigens including bacterial, fungal, viral, and chemical

  • Early phase: neutrophilic inflammation
  • Late phase: elevated TNF-α production and granuloma formation within lesions


  • Idiopathic (~50% of cases)
  • Bacterial:
    • β-hemolytic streptococcal infection is the most common trigger in children.
    • Bacterial enteritis (e.g.,Yersinia, Salmonella, Campylobacter)
    • Mycoplasma
    • Uncommon: cat-scratch disease, Chlaymdia trachomatis, brucellosis, rickettsial infections
  • Mycobacterial
    • Tuberculosis
    • Atypical mycobacteria
    • Leprosy
  • Viral
    • Epstein-Barr virus
    • HIV
    • Hepatitis B
  • Fungal
    • Coccidioidomycosis
    • Histoplasmosis
    • Inflammatory tinea capitis; kerion
  • Inflammatory disorders
    • Inflammatory bowel disease (cases with Crohn disease more common than cases with ulcerative colitis)
    • Sarcoidosis
    • Behçet disease
  • Pregnancy
  • Malignancy (leukemia, lymphoma)
  • Medications
    • Oral contraceptives
    • Sulfonamides
    • Phenytoin
    • Bromides and iodides

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