Clinicopathological findings of tubulointerstitial nephritis: a cross-sectional analysis of the Japan Renal Biopsy Registry (J-RBR).

Background: Tubulointerstitial nephritis (TIN) is an important disease involving a diverse set of factors that can cause both acute kidney injury and chronic kidney disease. The purpose of this cross-sectional study was to clarify the causative diseases and clinicopathological characteristics of TIN using the Japan Renal Biopsy Registry (J-RBR).

Methods: This cross-sectional study analyzed data from 22,049 cases registered in the J-RBR between 2018 and 2022. Clinicopathological findings at diagnosis were investigated.

Results: Of the enrolled cases, 913 were diagnosed with TIN. "Drug-induced" was the most common (232 cases, 25.7%), followed by "IgG4-related kidney disease" (124 cases, 13.7%). Of "Drug-induced" TIN cases, "Chemotherapy-related" was the most common cause (63 cases, 27.2%), including 47 cases of "immune checkpoint inhibitor (ICI)-associated" TIN. IgM-positive plasma cell-rich TIN (IgMPC-TIN), which has been the focus of much attention in recent years, was also included, with 9 cases.

Conclusions: This is the first report of the clinicopathological findings of TIN patients in a large-scale, nationwide registry of renal biopsies. It was possible to identify recent trends in causative diseases, including an increase in chemotherapy-related TIN and IgMPC-TIN.