Description

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

Epidemiology

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

Pathophysiology

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

Etiology

• 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