Abstract
Despite intense research, the underlying mechanisms and the etiology of Tourette’s syndrome (TS) remain unknown. Data from molecular imaging studies targeting the dopamine system in Tourette patients are inconclusive. For a better understanding of the striatal dopamine function in adult dopamine-antagonist-free patients we performed a systematic review in August 2017 identifying 49 PET and SPECT studies on the topic of TS. A total of 8 studies appraised the dopamine transporter (DAT) with 111 Tourette patients and 93 healthy controls, and could be included in a meta-analytic approach. We found a significantly increased striatal DAT binding in Tourette patients (Hedges' g = 0.49; 95% CI: (0.01–0.98)), although this effect did not remain significant after correcting for age differences between cohorts. A second meta-analysis was performed for the striatal dopamine receptor including 8 studies with a total of 72 Tourette patients and 71 controls. This analysis revealed a nonsignificant trend toward lower dopamine 2/3 receptor binding in striatum of Tourette patients. Other analyses regarding study population characteristics in both the DAT and receptor meta-analysis did not show any meaningful results. Our results indicate that dopaminergic alterations in TS are likely and thereby this data would be in line with the current pathophysiological hypotheses of a dysfunction in the dopamine system, e.g., the hypothesis of tonic-phasic dysfunction. However, these analyses suffer from low effect sizes probably due to the heterogeneity of TS and highlight the need for further large-scaled neuroimaging studies.
Highlights
Tourette’s syndrome (TS) is a heritable neuropsychiatric movement disorder, which is clinically characterized by the simultaneous presence of at least one vocal tic and multiple motor tics for at least 12 months[1]
Fourteen original positron emission tomography (PET) or single-photon emission computed tomography (SPECT) studies reflecting ligands to the striatal dopamine system in adult TS patients and matched healthy controls were included in this meta-analysis
For the analysis of the dopamine transporter (DAT) data from 6 SPECT and 2 PET studies comprising a total of 111 TS patients and 93 healthy controls were included
Summary
Tourette’s syndrome (TS) is a heritable neuropsychiatric movement disorder, which is clinically characterized by the simultaneous presence of at least one vocal tic and multiple motor tics for at least 12 months[1]. Most Tourette patients have associated neuropsychiatric comorbidities such as obsessive–compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD). Those affected frequently suffer from mood disorders or rage attacks[3]. Since the 1970s several classes of psychotropic drugs, especially dopamine-antagonists, have proven their efficacy in reducing frequency and severity of vocal and motor tics. There are only a limited number of randomized controlled trials for the pharmacological treatment of TS. This lack of evidence for safety and efficacy of pharmacotherapy leads to the absence of firm recommendations. The drugs commonly used are often associated with severe
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