IgG4-related kidney disease (IgG4-RKD) is a collective term used to describe the different types of renal involvement seen in IgG4-related disease (IgG4-RD). IgG4-RD is a recently described systemic immune-mediated disease that can involve nearly any organ system. The best-recognized form of IgG4-RKD is IgG4-related tubulointerstitial nephritis (IgG4-TIN), which may present as renal failure, renal mass lesions, or both. Radiographically, renal lesions are commonly bilateral and multiple, predominantly involving renal cortex, and can mimic a neoplasm. On tissue sections, IgG4-TIN is characterized by a plasma cell-rich interstitial inflammatory cell infiltrate, often with numerous eosinophils, and typically accompanied by storiform fibrosis; these features are strikingly similar to the fibroinflammatory lesions seen in other organs affected by IgG4-RD. In the majority of cases of IgG4-TIN, tubular basement membrane immune complex deposits, a useful feature to help distinguish IgG4-TIN from other forms of tubulointerstitial nephritis, can be seen by immunofluorescence or electron microscopy studies. The histopathologic, immunophenotypic, ultrastructural, and radiographic features of IgG4-related tubulointerstitial nephritis are reviewed here. Glomerular disease can also be associated with IgG4-RD, most commonly membranous glomerulonephritis, which may occur with or without concurrent IgG4-TIN.
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