18F-Fluorodeoxyglucose Positron Emission Tomography Imaging Assessment within a Randomized Controlled Trial in Giant Cell Arteritis.

Abstract

To compare FDG-PET imaging to clinical and laboratory-based assessments of disease activity in a randomized controlled trial (RCT) in giant cell arteritis (GCA). Patients with new-onset or relapsing GCA were randomized to guselkumab or placebo plus tapered glucocorticoids in an international, multicenter RCT. FDG-PET was performed at the baseline visit prior to randomization and repeated at disease flare or the Week 52 visit (clinical remission off glucocorticoids). FDG-PET scans were interpreted as active or inactive by two readers and the PET Vascular Activity Score (PETVAS) was calculated to quantify arterial FDG uptake. FDG-PET findings were compared to clinical assessment, acute phase reactants, and glucocorticoid use at each visit. Baseline FDG-PET scans were interpreted as active vasculitis in 28 (55%) of 51 patients. FDG-PET activity at enrollment was not associated with clinical symptoms, acute phase reactants, or risk of flare. Younger age (70 vs 76 years; p=0.03), and female sex (89% vs 48%, p<0.01) were significantly associated with increased FDG-PET activity. There were no differences in prior glucocorticoid dose (median 780mg) or duration (median 23 days) between patients with baseline active versus inactive FDG-PET scans. FDG-PET scans were active in 17/21 (81%) during clinical flare and in 14/20 (70%) at Week 52. Subsets of patients had persistently active (n=21) or inactive (n=9) PET scans at all timepoints, independent of clinical assessment. Vascular FDG-PET activity may be discordant with clinical assessment, particularly in subsets of patients with GCA. Imaging-based outcome measures should remain exploratory in future therapeutic trials.