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)
- β-hemolytic streptococcal infection is the most common trigger in children.
- Bacterial enteritis (e.g.,Yersinia, Salmonella, Campylobacter)
- Uncommon: cat-scratch disease, Chlaymdia trachomatis, brucellosis, rickettsial infections
- Atypical mycobacteria
- Epstein-Barr virus
- Hepatitis B
- Inflammatory tinea capitis; kerion
- Inflammatory disorders
- Inflammatory bowel disease (cases with Crohn disease more common than cases with ulcerative colitis)
- Behçet disease
- Malignancy (leukemia, lymphoma)
- Oral contraceptives
- Bromides and iodides
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