A 62-year-old woman presents with rapidly progressive glomerulonephritis and recurrent epistaxis. Biopsy of the kidney shows focal segmental necrotizing glomerulonephritis with crescents but no immune deposits on immunofluorescence, and lung biopsy shows capillaritis without granulomas. Which laboratory result is most likely?

• A Low serum complement with positive anti-dsDNA
• B Cytoplasmic ANCA directed against proteinase 3
• C Perinuclear ANCA directed against myeloperoxidase ✓
• D Positive antiglomerular basement membrane antibody titers

Explanation

Microscopic polyangiitis is a pauci-immune necrotizing vasculitis of small vessels associated with perinuclear ANCA against myeloperoxidase, and it commonly causes rapidly progressive crescentic glomerulonephritis with pulmonary capillaritis. The absence of granulomas separates it from granulomatosis with polyangiitis, which carries cytoplasmic ANCA against proteinase 3. Low complement with anti-dsDNA suggests lupus nephritis, which shows full house immune deposits.

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.