<scp>18F</scp> ‐Fluorodeoxyglucose Positron Emission Tomography Imaging Assessment Within a Randomized Controlled Trial in Giant Cell Arteritis

OBJECTIVE: To compare fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging to clinical- and laboratory-based assessments of disease activity in a randomized controlled trial (RCT) in giant cell arteritis (GCA). METHODS: 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 before 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 was calculated to quantify arterial FDG uptake. FDG-PET findings were compared to clinical assessment, acute phase reactants, and glucocorticoid use at each visit. RESULTS: 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 780 mg) or duration (median 23 days) between patients with baseline active versus inactive FDG-PET scans. FDG-PET scans were active in 17 of 21 (81%) patients during clinical flare and in 14 of 20 (70%) patients at week 52. Subsets of patients had persistently active (n = 21) or inactive (n = 9) PET scans at all time points, independent of clinical assessment. CONCLUSION: 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.