Objective: Clinical evidence indicates that the Tourette's syndrome (TS) is associated with hyperactivity of the dopaminergic system; however, imaging studies of dopamine transporter (DAT) in TS patients remain controversial. In this study, we aimed to study DAT binding capacities in a relatively larger sample of drug-naive patients with TS in comparison with controlled subjects by (99m)Tc-TRODAT-1 SPECT/CT imaging. We also aimed to look for any possible correlations between DAT and age, disease duration or tic severity of TS, which have not been thoroughly investigated in previous studies. We tried to provide more evidence for the understanding of the physiopathological mechanism of TS from the molecular imaging perspective.
Methods: Eighteen drug-naive patients with TS and 8 age- and gender-matched healthy subjects were recruited. Severity of TS was measured with Yale Global Tic Severity Scale. Brain SPECT/CT was performed 2.5 h after injection of (99m)Tc-TRODAT-1. Regions of interest were drawn on the striatum including its sub-regions of caudate and putamen. The cerebellum was used as the reference region. DAT uptake ratio was calculated by subtracting the mean counts per pixel in the cerebellum from the mean counts per pixel in the striatum, caudate or putamen and by dividing the result by the mean counts per pixel in the cerebellum. Comparisons of DAT uptake ratios between TS patients and controls, and comparisons in bilateral striatum and sub-regions in TS patients were carried out. Correlation analysis between DAT uptake ratios and clinical data were also conducted.
Results: TS patients showed significantly higher uptake of (99m)Tc-TRODAT-1 in bilateral striatum in comparison with the controls. There was no group-specific preferential lateralization in striatal uptake. DAT uptake ratios were not correlated with age and tic severity scores, but significant negative correlation with disease duration was found.
Conclusions: High level of DAT was demonstrated in drug-naive TS patients compared with normal controls, and it was negatively correlated with TS duration. Therefore, with the extension of the disease duration, certain degree of adaptation might occur in TS patients to compensate for the DAT increase, which suggested that hyper-functional DAT might be involved in the early pathophysiological changes of TS.