“When Linear Meets Fibrillary: A Rare Coexistence of Anti-GBM Disease and Fibrillary Glomerulonephritis”

Anti-glomerular basement membrane (anti-GBM) disease is a rare autoimmune disorder characterized by rapidly progressive glomerulonephritis (RPGN) with circulating antibodies directed against the glomerular basement membrane. Fibrillary glomerulonephritis (FGN) is an immune complex–mediated glomerular disease characterized by Congo red–negative fibrillary deposits and positive DNAJB9 staining with an incidence of 0.5% - 1%. Although crescentic transformation has been described in rare cases of FGN, the coexistence of FGN and anti-GBM disease is exceedingly uncommon. A 51-year-old woman with type 2 diabetes mellitus presented with rapidly progressive renal failure, edema and oliguria. Serum creatinine increased from 4.4 mg/dL to 7.9 mg/dL within days, requiring hemodialysis. Serologic evaluation demonstrated strongly positive anti-GBM antibodies (titer 71U/ml), while ANA by IF, ANCA by ELISA, anti-dsDNA, and complement levels were unremarkable. Kidney biopsy revealed necrotizing and crescentic glomerulonephritis with cellular and fibrocellular crescents. On immunofluorescence IgG(+3) shows linear positivity on glomerular basement membrane along with smudgy positivity on the mesangium. Light microscopy demonstrated PAS-positive, silver-negative mesangial deposits, and immunohistochemistry showed positive mesangial staining for DNAJB9, confirming concurrent FGN. The patient was treated with pulse methylprednisolone followed by oral corticosteroids, plasmapheresis, cyclophosphamide, and rituximab. Despite prompt immunosuppressive therapy, she remained dialysis-dependent. This case highlights a rare coexistence of anti-GBM disease and DNAJB9-positive FGN presenting as RPGN. Recognition of underlying FGN in patients with crescentic glomerulonephritis is important because it may influence disease classification, prognosis, therapeutic decisions, and future transplant planning. To our knowledge, this represents the first reported case of concurrent anti-GBM disease and FGN from India.