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Microscopic Polyangiitis — RACP Adult Medicine MCQ

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HardNephrologyMicroscopic PolyangiitisRACP Adult Medicine

A 65-year-old woman with a history of type 2 diabetes and CKD presents with bilateral foot drop and wrist drop. Nerve conduction studies confirm mononeuritis multiplex. Her ANCA is positive (MPO specificity). Urinalysis shows active sediment with red cell casts. Creatinine has risen from 120 to 280 µmol/L over 2 weeks. What is the most likely diagnosis?

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Correct answer: E — Microscopic polyangiitis

Mononeuritis multiplex with rapidly progressive glomerulonephritis and MPO-ANCA positivity (p-ANCA) is characteristic of microscopic polyangiitis (MPA). MPA is a small-vessel vasculitis that can affect kidneys (crescentic GN), nerves (mononeuritis multiplex), lungs (alveolar haemorrhage), and skin. Unlike GPA, it does not cause granulomatous inflammation or upper airway disease. Treatment is with cyclophosphamide (or rituximab) plus corticosteroids.

Reference: eTG – 2025 – Rheumatology; KDIGO – 2024 – ANCA Vasculitis Guidelines