Fibrillary Glomerulonephritis: Current Insights into Pathology, Pathogenesis, and Clinical Outcomes

Fibrillary glomerulonephritis (FGN) is a rare, predominantly glomerular disease characterized by non-amyloid fibrils measuring 10-30 nm in diameter, deposited in the glomeruli in a random, non-branching pattern. The diagnosis is supported by ultrastructural demonstration of randomly arranged fibrils, and DNAJB9 immunohistochemistry has improved diagnostic confidence in routine clinical practice. The recent discovery of DNAJB9 has significantly improved diagnostic accuracy through immunohistochemistry, reducing reliance on ultrastructural studies. FGN commonly presents with proteinuria, often in the nephrotic range, along with hematuria and varying degrees of renal dysfunction. Histologically, fibrillary glomerulonephritis exhibits a spectrum of patterns, including mesangioproliferative, membranoproliferative, diffuse proliferative, membranous, and diffuse sclerotic forms, with mesangioproliferative and membranoproliferative patterns being the most commonly encountered. Immunofluorescence typically reveals polyclonal IgG and C3 deposits. The disease is often idiopathic but may be associated with autoimmune conditions, infections, monoclonal gammopathy, or malignancy. FGN generally carries a poor prognosis, with many patients progressing to end-stage renal disease. This review summarizes recent advances in the understanding of FGN, including its pathology, pathogenesis, and clinical implications.