Background Takayasu arteritis (TA) is a large-vessel vasculitis predominantly affecting the aorta and its main branches. Assessing disease activity is difficult and mainly based on the clinical findings, levels of acute phase reactants and angiography, but these items generally do not correlate well

Objectives The aim of the this study was to investigate the role of PET/CT in the diagnosis of the disease and assessing disease activity in TA

Methods Thirty TA patients fulfilling ACR criteria underwent FDG-PET/CT were retrospectively assessed. Disease activity was defined according to NIH criteria. A nuclear physician who was blinded to clinical and laboratory data examined all PET/CT scans. PET/CT scans were considered negative if vascular FDG uptake was lower than liver uptake, if there was moderate (equivalent to that of liver) or marked (more than liver) FDG uptake in at least one vessel area, the scan was considered positive for vasculitis. The levels of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were measured concomitantly. The correlation between CRP and ESR with SUV_max values of vessels was investigated. Disease activity with the NIH cirteria, CRP levels and ESRs were compared in subjects with or without positive PET/CT scans. ROC curve analyses were performed to assess the sensitivity and specificity of CRP and ESR according to PET/CT positivity

Results PET/CT was performed for diagnostic purposes early in the disease course in 9 subjects and to assess disease flare in 21 subjects on follow-up. The rate of a positive PET/CT examination tended to be higher in diagnostic/early use (88.9% positive) compared with use for flare-assessment (61.9% positive), although the difference was not significant (Fisher=0.2). Median CRP and ESR tended to be higher in PET/CT positive patients compared with PET/CT negative subjects (median CRP 19 vs. 14, p=0.16; mean ESR 59.8±36.5 vs. 35.2±19.7, p=0.07). ROC curve analysis showed an ESR of 38 mm/h or higher was 68.4% sensitivity and 66.7% specificity to predict a positive PET/CT examination (positive and negative predictive values 81.6% and 50%). A CRP of 14.5 mg/L or higher was 66.7% and 55.6% specific to predict a positive PET/CT examination (positive and negative predictive values 77.8% and 41.7%). While CRP was significantly correlated with mean SUV_max value of aorta (r=0.41, p=0.02), ESR was weakly correlated with SUV_max value of aorta (r=0.3, p=0.13). There was moderate agreement between PET-CT and NIH criteria (kappa 0.462, p=0.01, sensitivity 81%, spesificity 67%).

Conclusions These results suggested that clinical benefit of PET/CT might be higher in diagnostic use (early in the disease course) compared with use for flare assessment (after treatment) in TA. There was a moderate association between NIH activity criteria and PET/CT activity. The predictive value of increased ESR and CRP was similar for a positive PET/CT scan with lower negative predictive values. CRP levels had a better correlation with SUV_max levels of aorta compared to ESR. PET/CT is a promising tool in the diagnosis and activity assessment of TA but discrepancies with other activity parameters do exist.

Disclosure of Interest None declared