Background
- Panniculitis (inflam. of subcutaneous fat
- Delayed hypersensitivity Rxn to a variety of antigens
- Painful, erythematous nodules, lower legs
- F:M = 6:1, 20-40 years old
- Self-limiting or recurrent
- Frequently assoc. systemic symptoms
Aetiology
- Idiopathic (30-50% of cases)
- Infections (˜30%):
- Streptococcal pharyngitis (˜20-30%)
- Tuberculosis (<5% in developed countries)
- Yersinia, EBV, Mycoplasma, Histoplasma
- Systemic diseases:
- Sarcoidosis (Löfgren's syndrome)
- IBD (Crohn's, UC) ˜10%
- Medications:
- Sulfonamides, oral contraceptives, penicillins (<5%)
- Other:
- Pregnancy (<5%)
Clinical
- Clinical Dx
- Nodules:
- Tender, erythematous
- 2-6 cm diameter, poorly demarcated
- Evolve over 1-2 weeks into bruise
- Resolve without ulceration/scarring
- Systemic features (with or preceding nodules)
- Fever, malaise
- Arthralgia
Differential Dx
- Cellulitis (common mimic; initially misdiagnosed in ˜25% of EN cases)
- Cutaneous vasculitis (e.g. polyarteritis nodosa)
- Lupus panniculitis
- Nodular fat necrosis
- Erythema induratum (tuberculous origin)
- Superficial thrombophlebitis
Investigations
A targeted work-up is essential and includes:
- Throat swab and ASO titre (Streptococcus)
- Chest X-ray (Sarcoidosis, TB)
- TB screening / Hx if suspected
- FBC, CRP, ESR
- Stool calprotectin ±colonoscopy (if IBD suspected)
- Urinalysis (if systemic vasculitis suspected)
- Β-HCG (if pregnancy is possible)
- Biopsy (rarely) = septal panniculitis without vasculitis
Management
- Supportive care: NSAIDs, rest, leg elevation, compression stockings
- ID / treat the underlying cause if found
- Self-limiting in most cases, resolving in 3-6 weeks
Prognosis
- Typically resolves without complications
- 30% of cases (underlying e.g. IBD/sarcoid)
- Prognosis excellent is underlying condition treated