ANCA-Associated Vasculitis: The Pulmonary-Renal Syndrome
ANCA-associated vasculitis (AAV), particularly granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA), is the primary vasculitis causing ground glass opacities with acute kidney injury—a presentation known as pulmonary-renal syndrome. 1, 2
Specific Vasculitis Types
The three main ANCA-associated vasculitides that cause this presentation are:
Granulomatosis with polyangiitis (GPA, formerly Wegener's): Most strongly associated with c-ANCA/PR3 antibodies (80-90% positive), commonly presents with upper respiratory tract involvement, pulmonary infiltrates/hemorrhage, and rapidly progressive glomerulonephritis 3, 4
Microscopic polyangiitis (MPA): Associated with p-ANCA/MPO antibodies (20-40% positive), typically presents with pulmonary-renal syndrome without upper airway involvement 3, 4
Eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss): Less commonly causes this presentation, associated with adult-onset asthma, eosinophilia, and can be ANCA-positive (35% with either c-ANCA or p-ANCA) 3, 1
Clinical Recognition
The combination of upper respiratory tract involvement, lower respiratory tract disease with ground glass opacities, constitutional symptoms, positive ANCA, and glomerulonephritis with RBC casts is diagnostic for severe GPA. 1
Key pulmonary features include:
- Ground glass opacities representing diffuse alveolar hemorrhage 1
- Hemoptysis and dyspnea 5
- Hypoxemia in severe cases 1
Renal manifestations include:
- Rapidly progressive glomerulonephritis with declining GFR over days to weeks 1, 2
- Microscopic hematuria with dysmorphic red blood cells and red cell casts 1
- Moderate proteinuria (1-3 g/day) 1
- Acute kidney injury meeting KDIGO criteria 6
Diagnostic Approach
Do not delay immunosuppressive therapy while awaiting kidney biopsy when clinical presentation strongly suggests AAV with positive ANCA serology, especially in rapidly deteriorating patients. 1
The diagnostic workup should include:
- High-quality antigen-specific immunoassays for MPO-ANCA and PR3-ANCA as the preferred screening method 1
- About 90% of patients with small-vessel vasculitis affecting the kidneys have ANCA, and a positive test with compatible clinical features is sufficient to begin treatment 1, 2
- Kidney biopsy remains the gold standard showing pauci-immune focal and segmental necrotizing and crescentic glomerulonephritis, with diagnostic yield as high as 91.5% in GPA 7, 1
- Lung biopsy has lower yield: only 12% of transbronchial biopsies positive for GPA, though open lung biopsies provide higher diagnostic yield 7
Immediate Management
The American College of Rheumatology recommends immediate initiation of remission induction therapy with rituximab or cyclophosphamide plus high-dose glucocorticoids in patients with severe, organ-threatening disease, without waiting for biopsy confirmation. 1
Specific treatment protocol:
- Rituximab is conditionally recommended for remission induction in severe GPA/MPA 1
- Cyclophosphamide 2 mg/kg/day for 3-6 months as alternative 1
- High-dose glucocorticoids: methylprednisolone 500-1000 mg IV daily for 3 days, followed by prednisone 1 mg/kg/day 1
- Plasma exchange should be considered in patients with severe acute kidney injury or diffuse alveolar hemorrhage with hypoxemia 1
Critical Pitfalls
Poor recovery of serum creatinine at 90 days is the strongest independent risk factor for both ESRD (RR=9.150) and all-cause death (RR=3.264) in AAV patients with AKI. 6
Additional risk factors for poor outcomes:
- KDIGO AKI stage 3 is an independent risk factor for ESRD (RR=3.116) 6
- Higher BVAS score predicts both renal endpoints and mortality 6
- Older age increases mortality risk 6
Patients with AAV should be managed in close collaboration with, or at, centers of expertise given the complexity of induction therapy, monitoring for treatment toxicity, and long-term relapse prevention. 7, 1