Association Between IgA Nephropathy and p-ANCA Vasculitis
The coexistence of IgA nephropathy (IgAN) and p-ANCA (MPO-ANCA) positivity is rare but clinically significant, occurring in approximately 1-3% of IgAN patients, and represents either true overlap disease or sequential development of both conditions rather than a direct pathogenic link 1, 2.
Key Clinical Characteristics of the Overlap
When ANCA positivity occurs in IgAN patients, several distinct features emerge:
Clinical Presentation
- Younger age at presentation compared to typical ANCA-associated vasculitis (AAV) patients (mean age ~23 years vs ~49 years) 3
- Rapidly progressive glomerulonephritis is the hallmark presentation, with ≥50% decline in eGFR over ≤3 months 1, 2
- Proteinuria typically around 1.5-3.4 g/day with dysmorphic microhematuria 2, 4
- Systemic vasculitis symptoms occur in approximately 50% of cases, though pulmonary hemorrhage is uncommon 2
- Higher ANA positivity rates compared to ANCA-negative IgAN 1
Histopathologic Features
The kidney biopsy reveals a hybrid pattern:
- Dominant IgA and C3 mesangial deposition (defining IgAN) 5
- Crescentic glomerulonephritis with necrotizing features (vasculitis-like lesions) 2, 3
- Lower percentage of fibrous crescents compared to pure AAV (0% vs 4%) 3
- Milder interstitial inflammation and fewer immune complex depositions than ANCA-negative IgAN 1
Critical Diagnostic Considerations
A repeat kidney biopsy is essential when established AAV patients develop new proteinuria and hematuria during maintenance therapy, as new-onset IgAN can develop years after initial AAV diagnosis 4. This case highlights that clinical deterioration in AAV should not automatically be assumed to represent disease relapse.
The diagnostic workup must include:
- MPO-ANCA and PR3-ANCA testing by both indirect immunofluorescence and chemiluminescence immunoassay
- ANA testing (independent risk factor for adverse outcomes in ANCA-positive IgAN) 1
- Kidney biopsy with immunofluorescence to distinguish true overlap from pure AAV
- Evaluation for extrarenal vasculitis manifestations
Treatment Approach
ANCA-positive IgAN with rapidly progressive features should be treated with the aggressive immunosuppressive protocols used for AAV, not standard IgAN therapy 2, 6.
Induction Therapy
Following the KDIGO 2024 AAV guideline framework 7:
- Glucocorticoids plus rituximab or cyclophosphamide (1B recommendation for AAV)
- For severe presentations (creatinine >4 mg/dL or rapid decline), cyclophosphamide plus glucocorticoids may be preferred given limited rituximab data in this setting 7
- The combination of rituximab and mycophenolate mofetil has shown efficacy in overlap cases 5
Maintenance Therapy
- Rituximab is preferred for maintenance, particularly in relapsing disease 7
- Mycophenolate mofetil represents a feasible alternative for overlap conditions 5
- Duration should follow AAV protocols (typically 2-4 years) rather than IgAN protocols
Important Caveats
- Standard IgAN therapies (RAS blockade, SGLT2 inhibitors, sparsentan, targeted-release budesonide) are not appropriate for rapidly progressive ANCA-positive IgAN 6
- The KDIGO 2025 IgAN guideline specifically states that rapidly progressive IgAN should be treated "in accordance with the KDIGO 2024 Clinical Practice Guideline for the Management of ANCA-Associated Vasculitis" 6
Prognosis and Risk Factors
Renal outcomes in ANCA-positive IgAN are similar to ANCA-negative IgAN when treated appropriately, with most patients responding positively to aggressive immunosuppression 1, 2, 3.
Independent risk factors for adverse renal outcomes in ANCA-positive IgAN include:
- Male sex
- ANA positivity (unique to this overlap)
- Higher baseline serum creatinine and proteinuria
- Severe tubular atrophy/interstitial fibrosis 1
Clinical Pitfalls to Avoid
- Do not delay treatment waiting for biopsy results when clinical presentation suggests rapidly progressive disease with positive ANCA serology 7
- Do not assume relapse in established AAV patients with new proteinuria/hematuria—consider repeat biopsy to identify new-onset IgAN 4
- Do not undertreate ANCA-positive IgAN with standard IgAN protocols—these patients require vasculitis-intensity immunosuppression 2
- Do not overlook ANA testing—it provides independent prognostic information in this overlap population 1
The mechanism underlying this association remains unclear and requires further investigation, but the practical management approach is well-defined: treat the vasculitic component aggressively while recognizing the underlying IgAN pathology 3.