Rapidly progressive proliferative glomerulonephritis with monoclonal immunoglobulin G deposits despite the mild histological changes

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits is characterized by granular deposits of monoclonal IgG; histologically it has typically a membranoproliferative or endocapillary pattern, and seen electronmicroscopically there are dense deposits without substructure. Here, we present the case of a 62-year-old Caucasian woman who was admitted with rapidly progressive kidney failure. The patient's status, the laboratory and imaging examinations did not support prerenal, postrenal and - among the intrinsic causes - vascular and tubulointerstitial origin. The proteinuria and dysmorphic microhematuria suggested rapidly progressive glomerulonephritis. Tests for anti-neutrophil cytoplasmic antibodies, anti-glomerular basement membrane, antinuclear antibodies and cryoglobulins were negative, the C3 and C4 levels were normal. The biopsy evaluation diagnosed proliferative glomerulonephritis with monoclonal IgG deposits because of mesangial granular deposits of IgG3-kappa, C3, and C1q, and ultrastructurally electron-dense deposits (incidence in our adult native kidney biopsy series: 0.18%). 31 glomeruli were assessed histologically. 29 glomeruli displayed mild mesangial hypercellularity, 2 glomeruli were globally sclerotic. Crescents were not observed. Mild arteriolar hyalinosis, interstitial fibrosis and tubular atrophy accompanied the glomerular alterations. In the postbiopsy evaluation, paraprotein or multiple myeloma was not detected. Despite the mild histological findings, the kidney failure progressed, and hemodialysis had to be started two weeks after the biopsy. Steroids, cyclophosphamide and rituximab did not affect her kidney function, and she remained on hemodialysis during the follow-up of 39 months. This report presents for the first time proliferative glomerulonephritis with monoclonal IgG deposits as the possible cause of rapidly progressive nephritic syndrome in the absence of pronounced glomerular proliferative, sclerotic or tubulointerstitial lesions.