IgG4-Related Disease with IgG1-Dominant Membranous Nephropathy: A Rare Case Report

Abstract

ABSTRACT Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated fibroinflammatory disorder affecting various organs and tissues. Kidney involvement in IgG4-RD commonly manifests as IgG4-related tubulointerstitial nephritis or IgG4-related membranous nephropathy, with the latter occurring less frequently. The identification of the phospholipase A2 receptor (PLA2R) antigen has improved our understanding of primary membranous nephropathy. Here, we present the case of a 60-year-old Chinese man initially diagnosed with IgG4-related pancreatitis, who achieved clinical remission with glucocorticoid therapy followed by low-dose glucocorticoid maintenance therapy. Two years later, the patient developed nephrotic syndrome. A kidney biopsy revealed membranous nephropathy characterized by glomerular subepithelial deposition of IgG1 and positive PLA2R staining. Rituximab (RTX) treatment resulted in complete clinical remission of nephrotic syndrome, and no recurrence was observed during the 24-month follow-up period. IgG4-RD complicated by membranous nephropathy is a rare pathological feature characterized by glomerular subepithelial IgG1 deposition and positive PLA2R antigen staining. In the present case, RTX treatment was effective in achieving clinical remission. These findings contribute to the evolving understanding of the relationship between IgG4-RD and membranous nephropathy.