Makindo Medical Notes

🔎 Introduction

• Microscopic Polyangiitis (MPA) is a small– to medium-vessel necrotising vasculitis.
• Distinctive features:
  • No granulomatous inflammation (unlike GPA / EGPA).
  • Few immune complex deposits → “pauci-immune” pattern.
  • Strongly associated with ANCA, most commonly MPO-ANCA (p-ANCA).
• Classified under the ANCA-associated vasculitides (AAV).

🧬 Aetiology & Pathogenesis

• Cause unknown, likely autoimmune with genetic + environmental triggers.
• Necrotising crescentic glomerulonephritis is the renal hallmark → rapid progression if untreated.
• Minimal immune complex deposition (distinguishes from lupus nephritis or IgA vasculitis).

🩺 Clinical Features

• Renal: Rapidly progressive GN → haematuria, proteinuria, rising creatinine.
• Skin: Palpable purpura, livedo, ulceration.
• Lungs: Pulmonary capillaritis → haemoptysis, diffuse alveolar haemorrhage (life-threatening).
• Nervous system: Mononeuritis multiplex or peripheral neuropathy.
• Eyes: Scleritis, episcleritis, or visual disturbance.
• Constitutional: Fever, weight loss, malaise, arthralgia.

🔬 Investigations

• Bloods: FBC, U&E (renal impairment common), CRP/ESR.
• Urine: Microscopic haematuria + proteinuria; red cell casts on microscopy.
• Serology: ANCA – typically MPO-ANCA positive (~70%).
• Imaging: CXR/CT → diffuse infiltrates or haemorrhage.
• Biopsy:
  • Renal biopsy → crescentic necrotising GN, pauci-immune on IF.
  • Skin/lung biopsy → necrotising vasculitis without granulomas.

🧪 Pathology Pearls

• Histology: Fibrinoid necrosis of vessel walls, crescents in glomeruli.
• Immunofluorescence: Negative or faint → “pauci-immune” pattern (exam buzzword).

💊 Management

• Induction (acute phase):
  • High-dose corticosteroids (IV methylprednisolone pulses → oral prednisolone).
  • + Cyclophosphamide or Rituximab (depending on patient profile/renal function).
  • Plasma exchange sometimes considered in severe pulmonary haemorrhage or rapidly progressive GN (though evidence is evolving).
• Maintenance:
  • Azathioprine, methotrexate, or mycophenolate once remission achieved.
  • Taper steroids gradually.
• Supportive: BP control, renal function monitoring, infection prophylaxis (e.g., PJP prophylaxis with co-trimoxazole if on cyclophosphamide/rituximab).

📈 Prognosis

• Without treatment → rapidly fatal due to renal or pulmonary failure.
• With treatment → 5-year survival >70%, but relapses are common.
• Long-term morbidity from renal impairment and immunosuppression side effects.

📚 Reference

• Microscopic Polyangiitis – Clinical Guidelines

💡 Teaching Pearl: If you see rapidly progressive glomerulonephritis + pulmonary haemorrhage + p-ANCA, think Microscopic Polyangiitis. Granulomas = GPA, Asthma/eosinophilia = EGPA.