Steroid-responsive nephrotic syndrome in a patient with proliferative glomerulonephritis with monoclonal IgG deposits with pure mesangial proliferative features

A 78-year-old woman developed acute-onset nephrotic syndrome. A renal biopsy showed mild mesangial proliferative glomerulonephritis. Immunofluorescence studies revealed granular IgG3- λ deposits within the mesangial area and along the glomerular capillary walls. Electron microscopy showed mesangial and subendothelial granular electron-dense deposits. The pattern of deposition was predominantly mesangial. Serum or urine monoclonal proteins were not detected. Middle-dose steroid therapy induced a rapid remission of nephrotic syndrome. We consider that this is the first case of steroid-responsive nephrotic syndrome due to an extremely rare glomerular disease, proliferative glomerulonephritis with monoclonal IgG deposits associated with pure mesangial proliferative features.