Association Between Baseline Aortic 18F-Fluorodeoxyglucose Uptake and Subsequent Aortic Dilatation in Giant Cell Arteritis: A Four-Year Post Hoc Analysis.

Background Large-vessel involvement is increasingly recognized in giant cell arteritis (GCA), with aortic inflammation detectable in a substantial proportion of patients at diagnosis. Structural complications, including progressive aortic dilatation, may develop during follow-up, yet it remains unclear whether increased aortic 18F-fluorodeoxyglucose (18F-FDG) uptake at diagnosis is associated with subsequent aortic dilatation in GCA. Objective To evaluate the relationship between baseline aortic 18F-FDG uptake measured by positron emission tomography/computed tomography (PET/CT) and subsequent ascending aortic dilatation, assessed as the progression in aortic diameter over time, in patients with biopsy-proven GCA. Methods A post hoc analysis was conducted in a prospectively followed cohort of 32 consecutive patients with newly diagnosed, biopsy-proven GCA; 25 patients with evaluable baseline and four-year follow-up imaging were included in the longitudinal structural analysis. All patients underwent baseline 18F-FDG PET/CT within three days of glucocorticoid initiation and contrast-enhanced computed tomography angiography (CTA) at diagnosis and after a mean follow-up of four years. Maximum standardized uptake values (SUVm) were measured in four predefined aortic segments, and aortic diameters were measured at the corresponding levels. Correlations between baseline SUVm and the change in aortic diameter were analyzed using Pearson's correlation coefficient. Results The mean ascending thoracic aortic diameter increased from 36.45 ± 4.7 mm at baseline to 38.15 ± 5.2 mm at four-year follow-up. Baseline SUVm in the ascending thoracic aorta correlated positively with the subsequent increase in diameter in the same segment (r = 0.490; p = 0.013), and global mean aortic SUVm also correlated with ascending aortic diameter progression (r = 0.436; p = 0.029). No significant correlations were identified in the other aortic segments. Conclusions Higher baseline aortic 18F-FDG uptake at the time of GCA diagnosis is associated with greater subsequent progression in ascending aortic diameter during follow-up. Baseline PET/CT findings may help identify patients who could benefit from closer structural aortic surveillance.