Epidemiology
Etiology
- Demographics: Young adults (20–40 y/o); strong female predominance (F:M ~ 5:1).
- Etiologies (“NO DRUGS” / High-Yield triggers):
- Infections:
- Group A Streptococcus (most common identifiable cause overall).
- Mycobacterium tuberculosis (TB).
- Endemic mycoses (Coccidioides [“desert rheumatism”], Histoplasma).
- Enteric pathogens (Yersinia, Salmonella, Campylobacter).
- Systemic diseases:
- Sarcoidosis (Löfgren syndrome: EN + bilateral hilar lymphadenopathy + polyarthralgia). c
- Inflammatory bowel disease (IBD) (Crohn disease > Ulcerative colitis; activity parallels bowel disease).
- Behçet syndrome.
- Drugs: Oral contraceptive pills (OCPs), penicillins, sulfonamides.
- Pregnancy.
- Idiopathic: ~50% of cases.
- Infections:
Pathophysiology
- Delayed hypersensitivity reaction → panniculitis (inflammation of subcutaneous fat)
Clinical features
- Nonspecific symptoms : fever, arthralgia , malaise, hilar lymphadenopathy
- Painful, subcutaneous nodules on both pretibial (anterior leg) surfaces (less common on other areas of skin)
- Firm, erythematous (1st week)
- Fluctuant (without suppuration) and bluish (2nd week)
- Progressively fades (i.e., yellow or brown hue)
Diagnostics
Treatment
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