Microscopic polyangiitis — SCE Rheumatology MCQ

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A 63-year-old woman presents with rapidly progressive glomerulonephritis, diffuse alveolar haemorrhage and palpable purpura on both legs. Urine microscopy shows red-cell casts. She is positive for MPO-ANCA and negative for PR3-ANCA. She has no asthma, blood eosinophilia, chronic sinonasal symptoms or other ENT disease. What is the most likely diagnosis?

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Correct answer: A — Microscopic polyangiitis

The diagnosis is microscopic polyangiitis. Rapidly progressive glomerulonephritis with red-cell casts, diffuse alveolar haemorrhage and purpura indicates a pulmonary–renal small-vessel vasculitis. MPO-ANCA positivity strongly favours MPA, while the absence of sinonasal disease, asthma and eosinophilia further supports it. GPA more often has PR3-ANCA and granulomatous upper-airway or pulmonary nodular disease. EGPA requires an eosinophilic phenotype, usually with asthma. Polyarteritis nodosa affects medium arteries and characteristically does not cause glomerulonephritis or pulmonary capillaritis. IgA vasculitis can cause purpura and glomerulonephritis, but this age, pulmonary–renal presentation and MPO-ANCA result favour an ANCA-associated vasculitis.

Reference: Suppiah R, et al. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology Classification Criteria for Microscopic Polyangiitis. Arthritis Rheumatol. 2022;74:400–406. https://pubmed.ncbi.nlm.nih.gov/35106973/