Abstract: The patient was a 63⁃year⁃old male. The clinical features included nephrotic syndrome with elevated serum creatinine and IgM lambda monoclonal band. Renal biopsy revealed mesangial proliferative glomerulonephritis with negative Congo red staining. Immunofluorescence on paraffin⁃embedded sections of renal tissues was negative for IgG subtype, C3 (-), IgM (+). Electron microscopy revealed abundant fibrillary deposits with a randomly arranged pattern in the mesangial area and glomerular basement membrane, measuring approximately 10-30 nm in diameter. Immunohistochemical staining for DNAJ heat shock protein family member B9 (DNAJB9) was positive, confirming the diagnosis of fibrillary glomerulonephritis associated with monoclonal gammopathy (IgM⁃LAMBDA). Management focused on blood pressure control and comprehensive care of chronic kidney disease aimed at preserving renal function.

Key words: font-family:Inter, -apple-system, BlinkMacSystemFont, ", font-size:16px, background-color:#F9FAFB, ">fibroid glomerulopathy, monoclonal immunoglobulinemia, mesangial proliferative glomerulonephritis, DNAJ heat shock protein family member B9