Tics are caused by alterations in prefrontal areas, thalamus and putamen, while changes in the cingulate gyrus reflect secondary compensatory mechanisms

Background: Despite strong evidence that the pathophysiology of Tourette syndrome (TS) involves structural and functional disturbances of the basal ganglia and cortical frontal areas, findings from in vivo imaging studies have provided conflicting results. In this study we used whole brain diffusion tensor imaging (DTI) to investigate the microstructural integrity of white matter pathways and brain tissue in 19 unmedicated, adult, male patients with TS "only" (without comorbid psychiatric disorders) and 20 age-and sex-matched control subjects. Results: Compared to normal controls, TS patients showed a decrease in the fractional anisotropy index (FA) bilaterally in the medial frontal gyrus, the pars opercularis of the left inferior frontal gyrus, the middle occipital gyrus, the right cingulate gyrus, and the medial premotor cortex. Increased apparent diffusion coefficient (ADC) maps were detected in the left cingulate gyrus, prefrontal areas, left precentral gyrus, and left putamen. There was a negative correlation between tic severity and FA values in the left superior frontal gyrus, medial frontal gyrus bilaterally, cingulate gyrus bilaterally, and ventral posterior lateral nucleus of the right thalamus, and a positive correlation in the body of the corpus callosum, left thalamus, right superior temporal gyrus, and left parahippocampal gyrus. There was also a positive correlation between regional ADC values and tic severity in the left cingulate gyrus, putamen bilaterally, medial frontal gyrus bilaterally, left precentral gyrus, and ventral anterior nucleus of the left thalamus. Conclusions: Our results confirm prior studies suggesting that tics are caused by alterations in prefrontal areas, thalamus and putamen, while changes in the cingulate gyrus seem to reflect secondary compensatory mechanisms. Due to the study design, influences from comorbidities, gender, medication and age can be excluded.