Differential Diagnosis of Leukocytoclastic Vasculitis
The differential diagnosis of leukocytoclastic vasculitis must distinguish between skin-limited disease versus systemic vasculitides, with the most critical considerations being ANCA-associated vasculitides (particularly Wegener's granulomatosis/GPA and microscopic polyangiitis), IgA vasculitis (Henoch-Schönlein purpura), cryoglobulinemic vasculitis, connective tissue diseases, and secondary causes including medications, infections, and malignancy 1.
Primary Systemic Vasculitides to Consider
The most important systemic vasculitides that present with leukocytoclastic vasculitis histology include:
ANCA-Associated Vasculitides: Wegener's granulomatosis (GPA), microscopic polyangiitis (MPA), and Churg-Strauss syndrome (CSS/EGPA) 2, 1. These carry significantly worse prognosis than isolated cutaneous disease and require aggressive immunosuppression 3.
IgA Vasculitis (Henoch-Schönlein Purpura): When IgA is the dominant immunoglobulin in immune complexes, systemic involvement is likely in both children and adults, with renal involvement being a key concern 4. IgA staining on biopsy specimens is diagnostic 1.
Cryoglobulinemic Vasculitis: Often associated with hepatitis C infection, requires checking cryoglobulins and hepatitis B/C serology 1, 3.
Hypocomplementemic Urticarial Vasculitis (HUV): Distinguished by urticarial lesions and low complement levels 1.
Connective Tissue Diseases: Particularly systemic lupus erythematosus (SLE) and subacute cutaneous lupus erythematosus (SCLE), which may have associated vasculopathy and coagulopathy 4.
Secondary Causes (Non-Vasculitic)
Drug-induced LCV is one of the most common causes and has favorable prognosis when the culprit medication is discontinued 1, 4. Multiple medications can trigger this, including paclizumab 5.
Infection-associated LCV includes:
- Bacterial infections and sepsis 4
- Hepatitis B and C viruses 1, 3
- Atypical respiratory pathogens like Chlamydia pneumoniae 6
- Parasitic infections such as hydatid disease in endemic regions 7
Malignancy-associated LCV must be considered, particularly in older patients 5, 1.
Critical Diagnostic Algorithm
When LCV is suspected based on palpable purpura, the following structured workup differentiates between these entities 1, 4, 3:
Mandatory Initial Testing:
- Skin biopsy with direct immunofluorescence: IgA deposition indicates IgA vasculitis; negative immunofluorescence suggests other etiologies 1, 4
- ANCA testing (both indirect immunofluorescence and ELISA for PR3 and MPO): Positive results indicate ANCA-associated vasculitis requiring expert management 2, 1
- Urinalysis and renal function: Proteinuria, hematuria, or elevated creatinine indicates systemic involvement requiring aggressive therapy 1, 4
- Complement levels (C3, C4): Low levels suggest cryoglobulinemic vasculitis or HUV 1, 3
- Hepatitis B and C serology: Essential for cryoglobulinemic vasculitis 1, 3
Additional Testing Based on Clinical Context:
- Antinuclear antibodies (ANA): For connective tissue diseases 1, 3
- Cryoglobulins and serum protein electrophoresis: If cryoglobulinemic vasculitis suspected 3
- Blood cultures and throat swabs: For infection-associated cases 4
- Complete blood count: Eosinophilia may suggest allergic granulomatosis 8
Key Prognostic Distinctions
A critical pitfall is assuming all LCV has the same prognosis. A patient with cutaneous LCV and moderate nephritis as a component of Henoch-Schönlein purpura has much better prognosis than a patient with identical findings as a component of Wegener's granulomatosis 3. This distinction fundamentally changes management from supportive care to aggressive immunosuppression.
IgG- or IgM-containing immune complex LCV has less systemic involvement and better prognosis than IgA vasculitis (HSP) 4. When LCV is drug-induced, prognosis is favorable and discontinuation is usually resolutive 1.
Systemic Involvement Assessment
Multiorgan involvement is common in primary systemic vasculitis 2. Look specifically for:
- Renal: Hematuria, proteinuria, rising creatinine (glomerulonephritis)
- Pulmonary: Hemoptysis, infiltrates on chest X-ray 8
- Gastrointestinal: Abdominal pain, nausea, vomiting 3, 6
- Musculoskeletal: Arthralgias, muscle weakness 3, 8
- Ocular: Decreased visual acuity 8
The presence of any systemic features mandates consideration of primary systemic vasculitis rather than isolated cutaneous disease and requires referral to centers with vasculitis expertise 2.