A 32-year-old woman presents with hemoptysis, bilateral nodular lung infiltrates, chronic sinusitis with nasal septal perforation, and rapidly rising creatinine. Renal biopsy shows pauci-immune crescentic glomerulonephritis. The serological finding most specific for this presentation targets which antigen?

• A Myeloperoxidase, giving a perinuclear staining pattern
• B Proteinase 3, giving a diffuse cytoplasmic staining pattern ✓
• C Collagen IV alpha-3 chain of the glomerular basement membrane
• D Glomerular endothelial cell phospholipids, detected as lupus anticoagulant activity

Explanation

Granulomatosis with polyangiitis is characterized by c-ANCA, antibodies directed against proteinase 3 in neutrophil primary granules, producing a diffuse granular cytoplasmic pattern on ethanol-fixed slides. The triad of upper airway destructive lesions, pulmonary nodules with cavitation or hemorrhage, and pauci-immune crescentic GN fits this diagnosis. Myeloperoxidase antibodies (p-ANCA) suggest microscopic polyangiitis, and collagen IV antibodies define anti-GBM disease, which would show linear IgG deposition on biopsy.

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.