Nivolumab-associated acute tubulointerstitial nephritis with IgG4-related kidney disease–like features in a patient with renal cell carcinoma

We report a case of nivolumab-induced acute tubulointerstitial nephritis with IgG4-related features in a patient with renal cell carcinoma. Kidney biopsy revealed marked interstitial inflammation with numerous IgG4-positive plasma cells but lacked storiform fibrosis and obliterative phlebitis, favoring ICI-associated acute tubulointerstitial nephritis with IgG4-rich inflammatory features rather than established IgG4-related kidney disease. Renal function improved rapidly after discontinuing the immune checkpoint inhibitor (ICI) nivolumab and initiating corticosteroid therapy. This report highlights an unusual presentation of ICI-associated acute interstitial nephritis with prominent IgG4-positive plasma cell infiltration and elevated serum IgG4 levels. These findings suggest that checkpoint blockade may induce an IgG4-rich inflammatory phenotype that overlaps with but does not fully meet the diagnostic criteria for IgG4-related kidney disease.