Idiopathic Fibrillary Glomerulonephritis: A Case Report Highlighting Diagnostic and Management Challenges

Fibrillary glomerulonephritis (FGN) is a rare glomerular disease characterized by non-branching fibrils within the glomerular basement membrane, often leading to progressive renal dysfunction. Despite advances in diagnostic methods, including DNA-J heat shock protein family member B9 (DNAJB9) immunostaining, the pathogenesis and optimal treatment strategies remain poorly defined. We present the case of a 55-year-old woman with longstanding microscopic hematuria and subnephrotic proteinuria who was diagnosed with idiopathic fibrillary glomerulonephritis (IFGN) following a renal biopsy. Histopathology revealed mesangial proliferation, thickened basement membranes, and focal crescent formation. Immunofluorescence microscopy demonstrated IgG positivity with kappa light chain restriction, while electron microscopy confirmed fibrillary deposits measuring 22 nm in diameter. DNAJB9 immunostaining was strongly positive, confirming the diagnosis. In the absence of an identifiable secondary cause, this case represents a rare instance of IFGN. The patient was managed with nephroprotective strategies, including renin-angiotensin system blockade, glycemic control, and lipid management. This case underscores the diagnostic and therapeutic challenges associated with IFGN and highlights the importance of early recognition, histopathological confirmation, and supportive management. Further research is essential to improve prognostic assessment and develop evidence-based treatments for this rare and progressive glomerular disease.