The real-world experience of combined cranial and large vessel 18F-FDG-PET/CT in the investigation of giant cell arteritis.

FDG-PET/CT offers high diagnostic accuracy in research settings for GCA, a systemic medium-large vessel vasculitis (M-LVV). We aimed to analyse its diagnostic performance in a real-world clinical setting. We audited all patients investigated with FDG-PET/CT for suspected new onset GCA between July 2019 and March 2022, at a single tertiary institution in Australia. Data was collected from patient and physician questionnaires, and scan reports describing FDG activity in cranial, supra-aortic, aortic and infra-aortic vascular territories, and the overall interpretation of the scan. The gold standard comparator in analysis was the unblinded treating physician's clinical diagnosis at a minimum of 6 months after the scan. One hundred thirty-five patients had an FDG-PET/CT as part of routine care in the investigation of suspected GCA. Forty-four (32.6%) patients had a clinical diagnosis of M-LVV. Thirty-five (26%) scans were reported as positive, 27 (20%) equivocal and 73 (54%) negative for active M-LVV. Diagnostic performance of FDG-PET/CT was dependent on the treatment of equivocal scans in binary analysis, with sensitivity ranging from 77.3 to 90.9% and specificity ranging from 75.8 to 98.9%. In cases with a clinical diagnosis of M-LVV, the supra-aortic territory was metabolically active in 31 (70.5%) and three had metabolic activity isolated to either the cranial or aortic regions. Combined cranial and large vessel FDG-PET/CT shows good diagnostic performance for GCA in a real-world setting. The supra-aortic territory was most commonly active in patients with M-LVV, yet assessment of all territories was required to maximise scan performance. Key Points • FDG-PET/CT has good diagnostic performance for GCA in the real-world setting. • Assessment of both cranial and large vessels is necessary to maximise FDG-PET/CT performance. • Equivocal FDG-PET/CT scans (20% of cases) can be further evaluated with ultrasound and/or biopsy.