Proliferative Glomerulonephritis With Monotypic Immunoglobulin Deposits: An Unusual Presentation in the Setting of Multiple Inciting Events Including COVID-19 Vaccination.

Proliferative glomerulonephritis with monoclonal immunoglobulin (mIg) deposits (PGNMID) is a rare glomerular disease characterized by glomerular deposits of mIg. The pathogenesis of PGNMID without circulating mIg is poorly understood but a role for aberrant immune response to infection or another exogenous stimulus has been proposed. We describe a unique case of PGNMID that presented with multiple episodes of acute kidney injury, nephritic syndrome, and hypocomplementemia, associated with self-limited febrile illnesses or COVID-19 vaccination. Monoclonal IgG lambda was detected in the serum and urine, consistent with monoclonal gammopathy of renal significance (MGRS). Consecutive kidney biopsies demonstrated evolving morphologic and immunohistologic features, with monotypic IgG lambda deposits identified only in the third biopsy. Despite the need for dialysis, renal dysfunction and hypocomplementemia resolved after each episode with corticosteroid therapy. This case illustrates infections or COVID vaccination maybe "second hits" that promote mIg deposition in PGNMID, possibly due to cytokine release by innate immune cells that promote endothelial cell injury.