Background PET has emerged as a promising diagnostic tool for the detection of large-vessel involvement in giant cell arteritis (GCA). In a recent meta-analysis including some heterogeneous studies, PET sensitivity and specificity for GCA diagnosis were 0.8 and 0.89, respectively. However, the lack of a standardised definition of vasculitis based on FDG uptake is one of the most important limitations in the diagnostic performance of PET. Atherosclerosis and vascular ageing highly influence FDG uptake, and may lead to vasculitis misdiagnosis.
Objectives To prospectively assess the utility of FDG-PET for GCA diagnosis in a cohort of newly diagnosed biopsy proven patients, using a ROC-analysis of FDG uptake at different vascular beds.
Methods From November 2006 to March 2011, all patients diagnosed at our institution were assessed for their potential participation in the study. The inclusion criteria were 1) newly diagnosed, biopsy-proven GCA, 2) fulfilment of at least 3 ACR classification criteria for GCA and 3) signed informed consent. Exclusion criteria included 1) lack of consent to participate, 2) severe hyperglycemia at the moment of PET performance and 3) treatment with corticosteroids for more than 3 days. The control group included patients with no chronic inflammatory diseases, matched for gender, age and traditional cardiovascular risk factors, who underwent PET for staging of lung cancer at early stage (with no metastases or contact with vascular structures). The standardized uptake value (SUV) was calculated at four aortic segments (ascending thoracic aorta, aortic arch, descending thoracic aorta and abdominal aorta), as well as at the supraaortic vessels (subclavian, carotid and axillary arteries) and the iliofemoral territory. Receiver–operator characteristics curves were used to calculate sensitivity and specificity at each vascular territory.
Results 30 patients and 20 controls were included. Mean SUV in each territory was significant higher in GCA patients than in controls. Mean SUV at supraaortic vessels showed the best area under curve (AUC) (0,826). According to this, a FDG uptake cut-off of 1,70 achieved a sensitivity and specificity of 81 and 79%, respectively, for GCA diagnosis (p<0,001). FDG uptake at the aorta showed a more limited utility (AUC = 0,740), with a sensitivity and specificity of 80 and 48, respectively, using a cut-off of 2,48 (p=0,001).
Conclusions Using an objective and reproducible FDG uptake cut-off, PET shows a remarkable sensitivity and specificity for the diagnosis of GCA. Supraaortic branches seem to be the most suitable vascular field for this purpose.
Supported by SAF 08/0438 and SAF 11/30073.
Disclosure of Interest None Declared
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