De Novo Proliferative Glomerulonephritis With Monoclonal Immunoglobulin Deposits (PGNMID) in a Renal Transplant Recipient.

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) represents a distinct glomerular pathology, classified under monoclonal gammopathy of renal significance (MGRS). In renal transplant, PGNMID usually develops as a recurrent disease, but can rarely arise de novo. Recurrence is relatively common, typically appearing within five to six months post-transplant, and is linked to poor graft outcomes. De novo PGNMID is exceedingly rare, with few reported in the literature. It generally presents in the late post-transplant period, with a more indolent clinical course and a variable response to immunotherapy. This case report is of a 50-year-old patient who had diabetic nephropathy as his native kidney disease. This report documents a unique instance of de novo PGNMID, occurring three years post-transplantation with persistent allograft dysfunction. The transplant kidney biopsy showed mesangial hypercellularity with immunoglobulin (Ig)G and kappa light chain deposition by immunofluorescence; however, electron microscopy was non-contributory due to the absence of viable glomeruli. Despite extensive evaluation, we could not identify any clone contributing to the MGRS in the bone marrow, nor could we identify any other evidence of lymphoproliferative disease on positron emission tomography-computed tomography (PET-CT). We managed the patient with empirical clone-directed therapy against a likely B-cell clone using Rituximab. During rituximab therapy, the patient developed E. coli urosepsis, which was managed successfully. At the last follow-up, graft function remained stable without progression, although the duration of follow-up is limited.