Immunoglobulin G4-related disease (IgG4-RD) is a systemic, immune-mediated fibro-inflammatory disorder with the potential to affect multiple organs, with the kidney being the most commonly involved organ, typically presenting as IgG4-related tubulointerstitial nephritis (IgG4-TIN). Anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (ANCA-GN), in contrast, is a pauci-immune necrotizing crescentic glomerulonephritis characterized by acute renal dysfunction and systemic inflammation. While early reports have interpreted IgG4-positive plasma cell infiltration in ANCA-associated vasculitis as evidence of overlap with IgG4-TIN, histologic resemblance in varying disease contexts can make differentiation challenging. In this context, we present the case of an 81-year-old woman diagnosed with both ANCA-GN and IgG4-TIN, informed by a comprehensive review of all previously reported cases. Renal biopsy confirmed this rare overlap, revealing pauci-immune crescentic glomerulonephritis alongside dense IgG4-positive plasma cell infiltration and storiform fibrosis. This case illustrates the diagnostic complexity posed by IgG4-rich inflammatory infiltrates in ANCA-associated disease and underscores the importance of careful clinicopathologic correlation to guide accurate diagnosis, appropriate immunosuppressive therapy, and improved understanding of potentially overlapping autoimmune mechanisms.
Qiu et al. (Tue,) studied this question.