Background: Fibrillary glomerulonephritis (FGN) is a rare primary glomerular disease that seldom coexists with\nother diseases. Membranoproliferative glomerulonephritis is a pathologic finding of renal lesions associated with\nIgM-secreting monoclonal proliferations. We present a case study of a patient with unusual simultaneous FGN and\nIgM-related renal disorder in nonmalignant monoclonal IgM gammopathy.\nCase presentation: A 63-year-old male presented with nephrotic syndrome and elevated serum creatinine levels.\nLaboratory examination revealed elevated levels of serum IgM and low C3 levels. Serum and urine immunofixation\nelectrophoresis showed a monoclonal IgM with a kappa light chain. A bone marrow biopsy revealed less than 5 %\nbone marrow infiltration by lymphoplasmacytic lymphoma, and a renal biopsy revealed mesangiocapillary\nglomerulonephritis on light microscopy. Immunofluorescent and immunohistochemical staining indicated granular\ndeposits of immunoglobulin G in the mesangium and granular deposits of immunoglobulin M and �º light chains\nalong the capillary wall. Electron microscopy revealed randomly arranged nonbranching fibrils of approximately\n15 nm in diameter in the glomerular mesangium and subendothelial electron-dense deposits. According to these\nresults, we confirmed FGN and membranoproliferative glomerulonephritis, which were attributed to monoclonal\nIgM deposits.\nConclusion: To the best of our knowledge, this is the first report of simultaneous FGN and membranoproliferative\nglomerulonephritis in nonmalignant IgM monoclonal gammopathy.
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