A 55-year-old man has rapidly progressive glomerulonephritis, alveolar hemorrhage, and palpable purpura. Renal biopsy shows focal segmental necrotizing glomerulonephritis with crescents and no immune deposits on immunofluorescence. No granulomas are seen. Serum testing will most likely show:

• A Anti-myeloperoxidase perinuclear ANCA (p-ANCA) ✓
• B Anti-proteinase 3 cytoplasmic ANCA (c-ANCA)
• C Anti-glomerular basement membrane antibody
• D Antinuclear antibody with anti-dsDNA specificity

Explanation

Microscopic polyangiitis is a pauci-immune necrotizing small-vessel vasculitis affecting arterioles, capillaries, and venules, associated with p-ANCA directed against myeloperoxidase. Unlike granulomatosis with polyangiitis, it lacks granulomatous inflammation and more commonly causes pulmonary capillaritis and rapidly progressive glomerulonephritis. Anti-PR3 c-ANCA points to GPA, and linear anti-GBM staining would indicate Goodpasture disease, distinguishing both from this granuloma-free, p-ANCA positive entity.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.