Proliferative glomerulonephritis with monoclonal immunoglobulin IgG1-κ deposition in a patient with type 1 diabetes: a case report and literature review.

Background: Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) is a rare glomerular disease characterized by edema, proteinuria, and renal insufficiency. No established treatment protocol is currently available. We report a case of PGNMID with monoclonal IgG1-κ deposits in a patient with a 19-year history of type 1 diabetes. Case presentation: A 30-year-old woman presented with a 1-week history of nausea, vomiting, and generalized edema. She had a 19-year history of type 1 diabetes mellitus with poor glycemic control. Three months before admission, she had been hospitalized for fever and was diagnosed with a urinary tract infection, during which her renal function was normal. After discharge, she continued to experience recurrent episodes of fever. One week before admission, she gradually developed generalized edema accompanied by decreased urine output. On admission, she was found to have nephrotic-range proteinuria, hypoalbuminemia, anemia, acute renal failure, and acute heart failure. After antimicrobial therapy, renal replacement therapy, and nutritional support, the patient underwent renal biopsy. Immunofluorescence showed diffuse, global, granular, and lumpy deposits of IgG, C3, and κ light chain along the glomerular capillary loops and in the mesangial regions, with strong IgG1 positivity. Electron microscopy revealed proliferation of glomerular capillary endothelial cells, accompanied by segmental mesangial matrix interposition into the basement membrane, resulting in a double-contour appearance. Segmental hump-like subepithelial electron-dense deposits were also observed. No abnormal monoclonal bands were detected by serum or urine immunofixation electrophoresis, and the serum and urine free light chain κ/λ ratios were within the normal range. Bone marrow aspiration revealed 0.5% plasma cells. The final diagnosis was proliferative glomerulonephritis with monoclonal IgG1-κ deposits (IgG1κ-PGNMID). The patient was treated with prednisone, cyclophosphamide, and renal replacement therapy, with a good initial response. She was temporarily weaned from renal replacement therapy in the short term, but subsequently required long-term maintenance dialysis. Conclusion: In patients with a long-standing history of diabetes, the presence of a preceding infection, hypocomplementemia, nephrotic-range proteinuria, and rapidly progressive renal dysfunction should prompt suspicion for non-diabetic kidney disease. In such cases, renal biopsy, together with serum and urine immunofixation electrophoresis, free light chain assays, complement testing, and rheumatologic autoantibody screening, is essential for the diagnosis and differential diagnosis of PGNMID and related disorders. For patients with confirmed PGNMID who lack clear evidence of monoclonality or decline targeted therapy, prednisone combined with cyclophosphamide may represent an effective alternative treatment option.