Is F18-FDG PET-CT a Reliable Diagnostic Tool for Immune Checkpoint Inhibitor-Associated Acute Interstitial Nephritis?

Background: Immune checkpoint inhibitor–associated acute interstitial nephritis (ICI-AIN) requires a kidney biopsy for a definitive diagnosis. A recent study suggested that 2-deoxy-2-[18F] fluoro-d-glucose positron emission tomography–computed tomography (F18-FDG PET-CT) may offer a noninvasive alternative, but lack of kidney biopsy in all patients and a proper control group receiving ICI therapy remained important limitations. We conducted the first study addressing these limitations and examined whether F18-FDG PET-CT could differentiate biopsy-proven ICI-AIN from other causes of AKI in patients on ICI therapy. Methods: This retrospective cohort study comprises 105 patients on ICI therapy who underwent F18-FDG PET-CT and had a kidney biopsy (Fig. 1A), along with data from a control group receiving ICIs without AKI. Patients with AKI were required to be off immunosuppression and have a PET-CT within 14 days before the biopsy or 10 days after it. A nuclear radiologist reviewed the PET-CTs and recorded the mean radiotracer standardized uptake value (SUVmean) in 5 regions of the renal cortex. Ratios of kidney SUVmean to blood pool and liver SUVmean were also calculated. Results: A total of 34 patients, all on ICI therapy were included (5 with ICI-AIN, 9 with AKI from other causes, and 20 without AKI). Kidney SUVmean did not differ significantly among the groups. ANOVA for the ratios of kidney SUVmean to liver and blood pool SUVmean showed significant differences. However, post hoc analysis revealed no significant differences between the ICI-AIN and the group with AKI from other causes for either ratio (Fig. 1B). Conclusion: Ratios of kidney SUVmean to blood pool and liver SUVmean may be useful indicators of AKI in patients receiving ICIs. However, the utility of F18-FDG PET-CT in differentiating underlying etiologies of ICI-associated AKI, such as AIN, remains limited. Funding: Private Foundation Support