Proliferative Glomerulonephritis With Monoclonal Immunoglobulin G Deposits (PGNMID) With Chronic-Type Thrombotic Microangiopathy (TMA): A Case Report.

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits (PGNMID) is a form of monoclonal gammopathy of renal significance. A pathological evaluation of a kidney biopsy is essential for the diagnosis of PGNMID because it is characterized by glomerulonephritis with exclusively glomerular monotypic immunoglobulin deposits, which are typically IgG, and less commonly IgM or IgA. Membranoproliferative glomerulonephritis and endocapillary proliferative glomerulonephritis are the typical pathological features of PGNMID. A 53-year-old Japanese woman presented with persistent proteinuria for more than 10 years. The patient had a medical history of unknown acute kidney injury 20 years previously and received a 1-year course of steroid therapy. She was later diagnosed with nephrosclerosis and received angiotensin II receptor blocker (ARB) therapy for over two years; however, her proteinuria gradually worsened, and renal function declined. A kidney biopsy revealed focal segmental endocapillary hypercellularity with mild mesangial proliferation and double contours of glomerular basement membranes. Immunofluorescence showed granular staining for IgG, C3, C1q, IgG3, and λ in the mesangial areas and along the glomerular capillary walls. Electron microscopy demonstrated electron-dense deposits without organized structures in the paramesangial and mesangial areas, together with subendothelial edema and new basement membrane formation. These findings did not conform to the typical membranoproliferative pattern, leading to a diagnosis of PGNMID with chronic thrombotic microangiopathy (TMA). In addition to ongoing ARB therapy, corticosteroid treatment reduced proteinuria and stabilized renal function. To our knowledge, this is a rare case of PGNMID that was accompanied by chronic TMA.