# F18-FDG PET–CT in immune checkpoint inhibitor-associated acute interstitial nephritis: what is the diagnostic value?

## TL;DR

This study evaluated whether F18-FDG PET–CT can noninvasively diagnose immune checkpoint inhibitor-associated kidney inflammation but found it unreliable for distinguishing it from other kidney injuries.

## Contribution

The first biopsy-validated study addressing limitations of prior work to assess PET–CT's diagnostic value for ICI-AIN.

## Key findings

- Renal SUVs did not differ significantly between ICI-AIN, other AKI causes, and controls.
- Serial PET-CTs showed a non-significant trend of increasing kidney SUVs in ICI-AIN from baseline to AKI.
- PET–CT could not reliably differentiate ICI-AIN from other AKI causes in this cohort.

## Abstract

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 biopsies 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 PET–CT could differentiate biopsy-proven ICI-AIN from other causes of acute kidney injury (AKI) in patients on ICI therapy.

This retrospective cohort study comprises 105 patients on ICI therapy who underwent F18-FDG PET–CT and had a kidney biopsy, along with data from a control group receiving ICIs without AKI. PET–CT scans were performed within 14 days before or 10 days after biopsy, and baseline PET-CTs obtained during ICI therapy before AKI, were reviewed by a blinded nuclear radiologist. Renal cortical standardized uptake values (SUV) were measured in five regions of interest, liver and blood-pool SUVs served as internal references.

Thirty-two patients were included (5 ICI-AIN, 7 AKI from other causes, 20 controls). Renal SUVs did not differ significantly among groups. In patients with serial PET-CTs, kidney SUVs tended to increase from baseline to AKI in ICI-AIN, but these changes were not statistically significant.

In this biopsy-validated cohort, PET-CTs did not reliably distinguish ICI-AIN from other causes of AKI in patients receiving ICI therapy. Larger prospective studies are needed to validate these findings.