A case of proliferative glomerulonephritis with monoclonal IgG3κ deposits accompanied by glomerular capillary microaneurysms.

Glomerular capillary aneurysms are distinctly rare and specific glomerular lesions characterized by aneurysmal dilatation of the glomerular capillaries. This formation is associated with glomerular capillary injuries with focal mesangiolysis. Here, we report a case of proliferative glomerulonephritis with monoclonal immunoglobulin G deposits (PGNMID) presenting with multiple glomerular capillary microaneurysms. A 53-year-old woman presented with persistent proteinuria and microhematuria. She had no underlying diseases, such as hematopoietic or lymphoproliferative disorders. A renal biopsy showed diffuse membranoproliferative lesions with foam cell infiltration and multiple microaneurysms of the glomerular capillary on light microscopy. Immunofluorescence analysis showed granular deposits of monoclonal immunoglobulin G3 kappa (IgG3κ), C1q, C3, and C4 in the glomeruli. Electron microscopy revealed different sizes of non-organized electron-dense deposits in the mesangial, subendothelial, and subepithelial areas. In addition, glomerular endothelial cells showed swelling and loss of fenestra or diffuse formation of fenestrated diaphragms, accompanied by irregular thinning of the glomerular basement membrane. Furthermore, immunostaining for CD31 (a marker for endothelial cell) and low-vacuum scanning electron microscopy study identified loss of endothelial cells in microaneurysm, suggesting severe glomerular endothelial cell injury. After a renal biopsy, only the medication for dyslipidemia was continued because there were no physical symptoms, such as edema, and urinary abnormalities continued with stable renal function. Further studies are needed to elucidate the pathogenesis of glomerular capillary injury in PGNMID and clarify the clinical and pathological characteristics of PGNMID with glomerular capillary microaneurysms.