Other features: palpable purpura (skin), mononeuritis multiplex (peripheral nerves), and sometimes GI vasculitis (abdominal pain). Upper respiratory tract involvement is notably absent (unlike GPA).
Order ANCA serologies: MPA is usually MPO-ANCA (p-ANCA) positive; also check anti-GBM to exclude Goodpasture's in pulmonary–renal cases.
Confirm with tissue biopsy (often kidney): shows pauci-immune necrotizing vasculitis (crescentic GN) without granulomas.
Determine disease severity (organ-threatening vs limited) – e.g., glomerulonephritis or alveolar hemorrhage necessitate aggressive therapy.
Do not delay treatment in severe disease: start high-dose steroids + cyclophosphamide/rituximab promptly to prevent irreversible damage.
alveolar hemorrhage + GN but linear IgG deposits (anti-GBM+); not ANCA-associated
Remission induction: high-dose corticosteroids + either cyclophosphamide or rituximab (for severe organ-threatening disease). Use methotrexate or MMF only in mild cases (no critical organ involvement).
Maintenance: after remission, switch to a less toxic agent for 1–2+ years (e.g., azathioprine or periodic rituximab) to prevent relapse.
Adjuncts: consider plasmapheresis if life-threatening renal or pulmonary failure (controversial); give PJP prophylaxis (TMP-SMX) during intensive immunosuppression.
MPA is typically MPO-ANCA positive (p-ANCA).
No ENT involvement or granulomas in MPA (distinguishes it from GPA).
Diffuse alveolar hemorrhage (hemoptysis, hypoxia, new infiltrates) → ICU-level emergency; requires immediate high-dose immunosuppression (risk of respiratory failure).
Rapidly progressive glomerulonephritis (quick rise in creatinine with RBC casts) → start aggressive therapy without delay to prevent irreversible renal failure.
Suspicion: patient with hematuria (± hemoptysis) and systemic inflammation → evaluate for ANCA-associated vasculitis.
Initial workup: send ANCA panel (MPO & PR3); check anti-GBM; get chest imaging if respiratory symptoms; basic labs (creatinine, UA).
Confirm diagnosis with biopsy of affected organ (often kidney) showing pauci-immune vasculitis (necrotizing GN).
If organ-threatening disease, begin induction therapy immediately (do not wait for biopsy) – high-dose steroids + cyclophosphamide or rituximab (consider plasma exchange for very severe renal failure).
After remission, continue maintenance immunosuppression (e.g., azathioprine or periodic rituximab) for 24–48 months; monitor for relapse.
Middle-aged adult with hemoptysis, dyspnea, rapidly rising creatinine, and p-ANCA positivity → microscopic polyangiitis (pulmonary–renal syndrome).
Patient with subacute hematuria, proteinuria, and anemia; kidney biopsy shows crescentic pauci-immune GN (ANCA-positive) → renal-limited microscopic polyangiitis.
Case 1
A 55‑year‑old man develops acute-onset hemoptysis and dark urine.
Case 2
A 63‑year‑old woman is evaluated for progressive fatigue and new-onset edema.
Kidney biopsy in microscopic polyangiitis: crescentic glomerulonephritis (H&E stain).
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