Simultaneous occurrence of fibrillary glomerulonephritis and renal lesions in nonmalignant monoclonal IgM gammopathy

BACKGROUND Fibrillary glomerulonephritis (FGN) is a rare primary glomerular disease that seldom coexists with other diseases. Membranoproliferative glomerulonephritis is a pathologic finding of renal lesions associated with IgM-secreting monoclonal proliferations. We present a case study of a patient with unusual simultaneous FGN and IgM-related renal disorder in nonmalignant monoclonal IgM gammopathy. CASE PRESENTATION A 63-year-old male presented with nephrotic syndrome and elevated serum creatinine levels. Laboratory examination revealed elevated levels of serum IgM and low C3 levels. Serum and urine immunofixation electrophoresis showed a monoclonal IgM with a kappa light chain. A bone marrow biopsy revealed less than 5 % bone marrow infiltration by lymphoplasmacytic lymphoma, and a renal biopsy revealed mesangiocapillary glomerulonephritis on light microscopy. Immunofluorescent and immunohistochemical staining indicated granular deposits of immunoglobulin G in the mesangium and granular deposits of immunoglobulin M and κ light chains along the capillary wall. Electron microscopy revealed randomly arranged nonbranching fibrils of approximately 15 nm in diameter in the glomerular mesangium and subendothelial electron-dense deposits. According to these results, we confirmed FGN and membranoproliferative glomerulonephritis, which were attributed to monoclonal IgM deposits. CONCLUSION To the best of our knowledge, this is the first report of simultaneous FGN and membranoproliferative glomerulonephritis in nonmalignant IgM monoclonal gammopathy.