Late Presentation of de Novo Proliferative Glomerulonephritis With Monoclonal IgG Deposits in a Renal Allograft: A Rare Case With an Unusual Clinical Course.

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) is a form of monoclonal gammopathy of renal significance (MGRS) in which monoclonal immunoglobulin deposits are found within the glomerulus, without involvement of other renal compartments. This condition can result in kidney dysfunction and ultimately kidney failure. It most commonly presents in the native kidney and has a high risk of recurrence in renal allografts, typically within a few months post-transplantation. PGNMID rarely presents as de novo in a transplanted kidney; if so, it usually manifests within 3 years. Early treatment is required to prevent further deterioration and reduce the risk of allograft loss. We present a case of a patient who presented with progressive kidney function decline 10.5 years after simultaneous pancreas-kidney (SPK) transplantation. The patient had a prior diagnosis of an immune complex-mediated glomerulonephritis on the pre-transplant native renal biopsy. The subsequent allograft biopsy showed electron-dense, glomeruli-limited deposits on electron microscopy, with immunofluorescence showing a nonspecific full-house pattern of staining. Immunofluorescence performed following protease (pronase) digestion on FFPE tissue showed the deposits to be IgG3 lambda light chain restricted, with no plasma cell or lymphoid clone identified in the bone marrow, resulting in a diagnosis of MGRS with a PGNMID pattern in the renal biopsy. This prompted treatment with prednisone and rituximab, with subsequent ongoing improvement in proteinuria and kidney function. To our knowledge, this is the latest presentation of post-transplantation de novo PGNMID with survival reported to date.