From Cough to Crisis: A Case of Proteinase 3-ANCA-Associated Vasculitis Presenting with Rapidly Progressive Glomerulonephritis in a 55-Year-Old Man

Introduction: PR3-ANCA glomerulonephritis is a pauci-immune vasculitis seen in granulomatosis with polyangiitis, presenting with respiratory symptoms, hematuria, and renal failure. Treatment includes steroids, immunosuppressants, and plasmapheresis. Case Description: A 55-year-old male with coronary artery disease, paroxysmal atrial fibrillation, and hyperlipidemia was admitted with a two-week history of cough, dyspnea, fever, arthralgia, hemoptysis, and epistaxis. Initially treated for presumed pneumonia with doxycycline, he showed no improvement and was hospitalized for intravenous antibiotics, later discharged on oral amoxicillin-clavulanate. He was readmitted with worsening respiratory symptoms. Chest CT ruled out pulmonary embolism but showed multifocal consolidations. Lab studies revealed acute renal failure, with serum creatinine rising from 0.8 mg/dL to 5.8 mg/dL. Urinalysis showed hematuria and proteinuria. Serology showed positive ANA and elevated PR3-ANCA (>8.0 U/mL), suggesting vasculitis. Bronchoalveolar lavage confirmed diffuse alveolar hemorrhage. Kidney biopsy revealed necrotizing glomerulonephritis and acute tubular necrosis. He was treated with corticosteroids, rituximab, and plasmapheresis. Discussion: PR3-ANCA–associated glomerulonephritis is a manifestation of small-vessel vasculitis, often linked with granulomatosis with polyangiitis (GPA). It is characterized histologically by pauci-immune necrotizing glomerulonephritis, typically without significant immune complex deposition. Clinically, it can present with a variety of symptoms, such as chronic sinusitis, hemoptysis, diffuse alveolar hemorrhage, and rapidly progressive renal dysfunction. Serologic tests often show elevated proteinase 3 anti-neutrophil cytoplasmic antibodies (PR3-ANCA), while renal biopsy confirms pauci-immune necrotizing glomerular inflammation. Treatment usually involves high-dose corticosteroids and immunosuppressive agents like rituximab or cyclophosphamide. In severe cases, particularly with pulmonary hemorrhage and rapidly worsening renal function, therapeutic plasma exchange may be considered to improve renal recovery and reduce the risk of progression to end-stage renal disease as compared to steroids alone.