Characteristic distribution of inflammatory lesions in IgG4-related kidney disease: Findings from autopsy case series

IgG4-related tubulointerstitial nephritis (TIN) reveals specific histologies such as storiform (“bird’s-eye pattern”) fibrosis, regional lesion distribution, and extension of inflammation into and beyond the renal capsule, all of which clearly serve to distinguish IgG4-related TIN from non-IgG4-related TIN. However, the histological extent of IgG4-related TIN in the kidney remains unclear, largely because histological analyses of IgG4-related TIN to date have been based generally only on renal needle biopsy specimens. We histologically analyzed five autopsy specimens of IgG4-related TIN cases. The lymphoplasmacytic infiltration or fibrosis was mainly located in the cortex and perivasculature. Notably, inflammation or fibrosis generally appeared prominently around the interlobar, arcuate and interlobular arteries or veins. In addition, all specimens included various stages of fibrosis in the same kidneys. Storiform fibrosis (bird’s-eye pattern fibrosis) was limited to the cortex. These results indicate that inflammation or fibrosis is predominantly located in the renal cortex and perivasculature in IgG4-related TIN. Of note is that the lesions showed a predilection to develop around medium- and small-sized arteries in addition to forming nodular lesions in the renal cortex.