Potential clinical utility of quantitative 18F-FDG PET/CT parameters in evaluating vascular inflammation in giant cell arteritis.

We aim to evaluate the utility of two novel quantitative PET/CT-derived parameters, Total Inflammatory Vascular Volume (TIVV) and Total Inflammatory Glycolysis Volume (TIGV), in assessing disease activity, treatment response, and predicting relapse in patients with large-vessel giant cell arteritis (LV-GCA). Three LV-GCA patients underwent baseline and serial follow-up 18F-FDG PET/CT scans. Disease activity was assessed using conventional visual methods (Meller's scale and PETVAS) and the novel quantitative parameters TIVV and TIGV, calculated using a semiautomated method based on FDG uptake thresholds relative to liver SUVmean. In Case 1, treatment initially deemed ineffective by visual criteria showed the greatest reduction in inflammatory burden using TIVV/TIGV. In this patient, the application of quantitative parameters could have prevented multiple ineffective treatment changes. In Case 2, increasing TIVV and TIGV values preceded clinical relapse, which was undetected by visual assessment. In Case 3, declining quantitative values, despite persistent visual hypermetabolism, supported our decision to continue therapy and aligned with clinical remission. In all cases, TIVV and TIGV provided an earlier and more accurate assessment of vascular inflammation than traditional methods. Therefore, TIVV and TIGV may offer more accurate and standardized measures for evaluating disease activity and guiding treatment in LV-GCA. These metrics could address limitations of current visual and semiquantitative approaches but warrant validation in large studies.