Double Trouble: Dual Positivity for Antiglomerular Basement Membrane Antibody and proteinase-3-antineutrophil Cytoplasmic Antibody Presenting as Rapidly Progressive Glomerulonephritis

Antiglomerular basement membrane (anti-GBM) disease and antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis are uncommon causes of rapidly progressive glomerulonephritis. Their coexistence, termed double-positive disease, is rare and associated with severe renal and pulmonary manifestations. A 27-year-old male came with complaints of inflammatory polyarthralgia followed by progressive dyspnea and hemoptysis. Investigations revealed azotemia, active urinary sediment with proteinuria, bilateral pulmonary infiltrates, and dual seropositivity for anti-GBM antibodies and proteinase-3-ANCA. A diagnosis of double-positive vasculitis with pulmonary-renal syndrome was made. The treatment of the patient started with intravenous methylprednisolone, therapeutic plasma exchange, and intravenous cyclophosphamide, followed by oral glucocorticoids. Renal function improved significantly, with serum creatinine decreasing from 2.44 mg/dL at presentation to 1.42 mg/dL at discharge. The patient remained clinically stable during follow-up. Double-positive anti-GBM and ANCA disease represents a distinct clinical entity with overlapping features of both conditions. Early recognition and aggressive immunosuppressive therapy can result in favorable renal outcomes.