Proliferative Glomerulonephritis With Monoclonal IgG Deposits: Another Unusual Presentation

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits (PGNMID) is a relatively rare diagnosis with variable presentation. When detectable, the disease is typically indolent rather than malignant and recurs in transplant cases. Here, we report a case of PGNMID, which presented clinically as rapidly progressive glomerulonephritis (RPGN). The patient presented to his primary care physician's office with diarrhea for one day and was admitted for acute kidney injury. Urine sediment was active, and the patient had nephrotic range proteinuria. Serologic workup was negative for any monoclonality: ANA, c-ANCA, and p-ANCA. Kidney biopsy showed diffuse proliferative and crescentic glomerulonephritis with IgG3-kappa restricted deposits, consistent with PGNMID. The patient required dialysis initiation, and corticosteroids were administered. The patient declined further immunomodulatory treatment and remains hemodialysis-dependent. This case highlights the potential for severe renal damage from monoclonal proteins despite an indolent or even undetectable hematologic clone. This entity needs further studies to better understand its immuno-physiological background and develop a standard treatment regimen.