Tubulointerstitial diseases: an updated framework for diverse and emerging entities

Tubulointerstitial diseases represent a heterogeneous group of kidney diseases with diverse causes and overlapping histopathologic and immunophenotypic patterns. Unlike glomerular disease, tubulointerstitial diseases have lacked specificity and standardized classification, but greater diagnostic precision is now possible and is necessary as nephrology enters an era of personalized medicine. This review provides an updated etiologic and attributive framework for tubulointerstitial nephritis/nephropathy (TIN) and tubular injury with 8 categories: drug effect, autoimmune/immune-mediated, infection-associated, hereditary/genetic, toxic/metabolic, monoclonal protein-associated, mimics of TIN, and idiopathic/other, recognizing overlap between these forms. This review highlights recently described or elucidated tubulointerstitial diseases such as immune checkpoint inhibitor-associated TIN, IgG4-related TIN, IgM plasma cell TIN, and VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome. The milestones of IgG4-related TIN exemplify how a TIN disease entity evolves and can serve as a model for the recognition of new TIN entities. Looking forward, new biopsy-based technologies, digital pathology, and artificial intelligence can refine classification, enable precision diagnostics, and help to discover new entities. Continued collaborative efforts will be required to translate these advances into clinical practice and improved outcomes.