Vasculitic Causes of Necrotizing Cellulitis
The primary vasculitic disorders that can present with necrotizing cellulitis are ANCA-associated vasculitides (AAV), specifically granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA), which cause necrotizing inflammation of small vessels including skin capillaries and arterioles 1.
Primary Vasculitic Causes
ANCA-Associated Vasculitides (Most Common)
Small-vessel vasculitides are characterized by necrotizing inflammation of arterioles, capillaries, and venules with little or no immune complex deposition (pauci-immune pattern). The three main subtypes that affect skin are:
- Granulomatosis with polyangiitis (GPA) - formerly Wegener's granulomatosis
- Microscopic polyangiitis (MPA)
- Eosinophilic granulomatosis with polyangiitis (EGPA) - formerly Churg-Strauss syndrome
These conditions commonly involve the skin along with upper/lower respiratory tract, eyes, kidneys, and nervous system 1, 2.
Medium-Vessel Vasculitis
Polyarteritis nodosa (PAN) affects medium-sized vessels and frequently presents with cutaneous manifestations including nodules and livedo reticularis, though true necrotizing cellulitis is less common than with small-vessel disease 3.
Distinguishing Features from Infectious Necrotizing Fasciitis
Critical distinction: True necrotizing fasciitis from bacterial infection (discussed in 4) presents differently than vasculitic necrotizing skin involvement:
- Infectious necrotizing fasciitis: Polymicrobial infection with gas formation, rapid progression over hours, "wooden" feel to tissues, requires emergent surgical debridement
- Vasculitic necrotizing cellulitis: Pauci-immune inflammation, associated with systemic symptoms (fever, weight loss), ANCA positivity in 90% of cases, responds to immunosuppression rather than antibiotics alone
Diagnostic Approach
When vasculitis is suspected as the cause of necrotizing skin changes:
- Check ANCA serology immediately - MPO-ANCA or PR3-ANCA positive in ~90% of AAV cases 1
- Obtain skin biopsy showing necrotizing vasculitis with neutrophilic infiltration and fibrin thrombi 5
- Assess for systemic involvement: Check urinalysis (hematuria, proteinuria), creatinine, chest imaging, and inflammatory markers 1
Important caveat: ANCA can be negative in 10% of cases, particularly in limited disease, so negative serology does not exclude vasculitis 1.
Rare Infectious Mimics
While the question asks about vasculitis, be aware that certain infections can cause vasculitis-like necrotizing cellulitis:
- Cryptococcus neoformans can cause necrotizing vasculitis with vascular invasion in immunocompromised patients 6, 7
- Bacterial septic vasculitis from systemic bacteremia can present with localized necrotizing cellulitis 5
These are infectious causes that secondarily produce vasculitis, not primary vasculitic disorders.
Treatment Implications
If vasculitis is confirmed, do not delay immunosuppression while awaiting biopsy results if clinical presentation and positive ANCA support the diagnosis 1. Standard induction therapy includes:
- High-dose glucocorticoids combined with either rituximab or cyclophosphamide
- Duration: 3-6 months induction, followed by 12-48 months maintenance therapy 1, 8
Key pitfall: Mistaking vasculitic necrotizing cellulitis for infectious necrotizing fasciitis and pursuing only surgical debridement without immunosuppression will result in treatment failure and potential mortality from untreated systemic vasculitis.