We acquired diffusion-weighted data at 1.5 T in nineteen adult patients fulfilling the DSM-IV-TR criteria for Tourette syndrome and in a healthy control group.
Diffusion tensor imaging (DTI) analysis in our adult TS sample shows a decrease of FA and increase in radial diffusivity in the corticospinal tract. There are widespread changes (reduced FA and increased radial diffusivity) in the anterior and posterior limb of the internal capsule. Furthermore, it confirms prior findings of altered interhemispheric connectivity as indicated by a FA-decrease in the corpus callosum. In addition, our results indicate that TS is not restricted to motor pathways alone but affects association fibres such as the inferior fronto-occipitalis fascicle, the superior longitudinal fascicle and fascicle uncinatus as well.
Tics are the hallmark of Tourette syndrome, so the involvement of the corticospinal tract fits in well with clinical symptoms. Cortical regions as well as limbic structures take part in the modulation of tics. Our findings of alterations in long association fibre tracts and the corpus callosum are a potential source for hindered interhemispheric and transhemispheric interaction. The change in radial diffusivity points toward a deficit in myelination as one pathophysiological factor in Tourette syndrome.