Microscopic Polyangiitis✅
🩺 Microscopic Polyangiitis (MPA) is a small- to medium-vessel necrotising vasculitis characterised by pauci-immune inflammation and strong MPO-ANCA (p-ANCA) association. Rapid recognition is crucial to prevent irreversible renal and pulmonary damage. ✅ NICE-compliant guidance applied
📖 About
- Part of the ANCA-associated vasculitides (AAV), alongside GPA and EGPA.
- Does not form granulomas (unlike GPA or EGPA).
- Renal involvement is common; pulmonary capillaritis occurs in 30–50% of adults.
🧬 Pathophysiology
- Autoimmune endothelial injury → necrotising inflammation of small vessels.
- Renal hallmark: crescentic glomerulonephritis → rapidly progressive if untreated.
- Pauci-immune: minimal immune complex deposition (distinguishes from lupus nephritis or IgA vasculitis).
- Likely triggers: genetic susceptibility + environmental factors (e.g., infection, drugs).
🩺 Clinical Features
- Renal: Haematuria, proteinuria, rising creatinine, rapidly progressive glomerulonephritis.
- Skin: Palpable purpura, livedo reticularis, ulceration.
- Lungs: Pulmonary capillaritis → haemoptysis, diffuse alveolar haemorrhage (life-threatening).
- Neurological: Mononeuritis multiplex, peripheral neuropathy.
- Eyes: Scleritis, episcleritis, visual disturbance.
- Constitutional: Fever, malaise, weight loss, arthralgia.
🔬 Investigations
- Bloods: FBC, U&E, CRP/ESR; renal function often impaired.
- Urine: Microscopic haematuria, proteinuria; red cell casts on microscopy.
- Serology: ANCA – typically MPO-ANCA (p-ANCA) positive ~70%.
- Imaging: CXR or CT chest for infiltrates or pulmonary haemorrhage.
- Biopsy:
- Renal biopsy → crescentic necrotising GN, pauci-immune on IF.
- Skin/lung biopsy → necrotising vasculitis without granulomas.
💊 Management
- Induction (acute phase):
- High-dose corticosteroids (IV methylprednisolone → oral prednisolone taper).
- + Cyclophosphamide or Rituximab (based on renal function and comorbidities).
- Plasma exchange in severe pulmonary haemorrhage or rapidly progressive GN (case-dependent, evidence evolving).
- Maintenance:
- Azathioprine, methotrexate, or mycophenolate after remission.
- Gradual steroid tapering.
- Supportive care: Blood pressure control, renal monitoring, infection prophylaxis (e.g., PJP if on immunosuppression).
📈 Prognosis
- Without treatment: rapidly fatal (renal or pulmonary failure).
- With treatment: 5-year survival >70%; relapses common.
- Long-term morbidity: renal impairment, side effects of immunosuppressants.
💡 Teaching Pearl: Rapidly progressive GN + pulmonary haemorrhage + p-ANCA strongly suggests MPA. Granulomas = GPA; asthma/eosinophilia = EGPA.
📚 References
