Comorbid Obsessive Compulsive Disorder in Tourette's Syndrome: Questioning its Impact

The article by Mahjoub et al1 constitutes an original contribution to using transcranial direct current stimulation (tDCS) to treat Gilles de la Tourette Syndrome (TS). Mahjoub et al1 provided valuable insights into the feasibility and tolerability of short-term SMA-targeted neuromodulation, which marks promising avenues for new treatment options for TS. Despite their small sample size, Mahjoub et al1 produced encouraging results. However, comorbidity could insert particular noise in interpreting the results. When comparing comorbidity proportions in the two arms, in Table 1, the presence of anxiety and/or depressive disorder is comparable between the two, as is the case for attention deficit hyperactivity disorder. Nevertheless, for obsessive-compulsive disorder (OCD), the sham contains three participants, whereas the active condition contains seven participants. This difference is significant when compared to the other comorbidities. Given that each arm only contains 12 participants, this imbalance makes it harder to accurately compare the assessment of tDCS efficacy for TS between the sham and active conditions. It becomes particularly relevant when looking into the significant effect of tDCS intervention on decreasing premonitory urge intensity. The authors suggest that the observed reduction in the Premonitory Urge for Tics Scale (PUTS) score after repeated stimulation in the active condition may be related to the role of the SMA, cingulate cortex, and insula in generating premonitory urges. While this is a plausible explanation, another one could be of interest. While the PUTS questionnaire has relatively good construct validity and internal consistency,2, 3 its discriminant validity is less robust. Studies in both adolescents and adults with varying TS severity have found associations and significant correlations between premonitory urges and OCD symptoms.2, 4, 5 This is often attributed to the fact that some aspects of premonitory urges closely resemble compulsions. Specifically, the overlap is most visible in “not just right” experiences and feelings of incompleteness items of the PUTS.2, 4, 5 Given that the majority of OCD comorbidity in the total sample was in the active group, it is reasonable to question whether the observed reduction in premonitory urge intensity was genuinely attributable to the tDCS intervention's effect on tic severity. Admittedly, the study's absence of significant differences in Y-BOCS scores, despite the imbalance of comorbid OCD in groups, could suggest that the tDCS intervention did indeed correctly target TS. However, one inclusion criterion of the sample was to remain clinically stable in any psychiatric comorbidity. This measure suggests that OCD comorbidities included in the sample could have been milder, explaining why the Y-BOCS questionnaire was not sensitive to significant changes in severity scores, whereas PUTS may have picked up on those changes. In light of this, it would be very interesting if there was a more pronounced reduction in the “not just right” experiences and feelings of incompleteness items of the PUTS. Despite these limitations, this initial study marks an important step forward in exploring new tDCS treatment options for TS. Non-invasive brain stimulation methods offer a promising combination of accessibility and potential efficacy for this disorder, especially in patients with higher symptom severity. (1) Research project: A. Conception, B. Organization, C. Execution; (2) Manuscript Preparation: A. Writing of the first draft, B. Review and Critique. L.H.: 1A, 1B, 1C, 2A. M.E.L.: 2A, 2B. Ethical Compliance Statement: The authors confirm that the approval of an institutional review board and patient consent was not required for this work. We also confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. Funding Sources and Conflict of Interest: No specific funding was received by MEL or LH for this work. MEL was supported by a project grant from the Canadian Institute for Health Research. Both authors declare no conflicts of interest relevant to this work. Financial Disclosures for the Previous 12 Months: MEL and LH have no disclosures to report. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

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