Towards an optimal semiquantitative approach in giant cell arteritis: an 18F-FDG PET/CT case-control study

Giant cell arteritis (GCA) is the most common form of vasculitis in western countries. F-18-FDG PET has been shown to be a valuable tool for the diagnosis of extracranial GCA, but results of studies are inconsistent due to a lack of standardized F-18-FDG PET criteria. In this study, we compared different semiquantitative approaches using a controlled design to define the most efficient method. All patients with biopsy-proven GCA who had undergone an F-18-FDG PET/CT scan in our PET unit were reviewed and matched with a control group based on age and sex. Different semiquantitative arterial (ascending and descending thoracic aorta and aortic arch) to background (liver, lung and venous blood pool) SUV ratios were blindly compared between GCA patients and matched controls. We included 11 patients with biopsy-proven GCA cases and 11 matched controls. There were no differences between the groups with regard to body weight, injected radioactivity, blood glucose level or CRP. The arterial to venous blood pool ratios discriminated the two groups better than other methods when applied to the aortic arch and the descending thoracic aorta (p < 0.015). In particular, the highest aortic to highest blood pool SUVmax ratio, when applied to the aortic arch, provided optimal diagnostic performance (sensitivity 81.8 %, specificity 91 %, AUC 0.87; p < 0.0001) using a cut-off value of 1.53. Among all tested F-18-FDG PET/CT methods, the aortic to blood pool SUVmax ratio outperformed the liver and lung ratios. We suggest the use of this ratio for the assessment of aortic inflammation in GCA patients.