A 45-year-old man with refractory sinusitis and hemoptysis has a chest radiograph showing nodular infiltrates and cavitation. Renal biopsy shows pauci-immune crescentic glomerulonephritis. Serum testing shows antibodies producing a diffuse granular cytoplasmic pattern on ethanol-fixed neutrophils. The target antigen is:
- A Myeloperoxidase (MPO)
- B Proteinase 3 (PR3) ✓
- C Double-stranded DNA
- D Glomerular basement membrane type IV collagen alpha-3 chain
Correct answer: B. Proteinase 3 (PR3)
Explanation
Granulomatosis with polyangiitis (Wegener) is strongly associated with c-ANCA, antibodies against proteinase 3 that give a diffuse granular cytoplasmic staining pattern on ethanol-fixed neutrophils. The triad of necrotizing granulomatous vasculitis of the upper and lower respiratory tract, renal pauci-immune crescentic GN, and c-ANCA fits this vignette. MPO antibodies (option A) produce a perinuclear pattern and are typical of microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis, while option D defines anti-GBM disease.
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.