Objective: To investigate the effect of cathodal transcranial direct current stimulation (tDCS) over the supplementary motor area (SMA) on tic severity in Tourette syndrome (TS).

Background: tDCS is a non-invasive method using a small direct electrical current to modulate cortical excitability. A limited number of small studies have explored tDCS as a potential treatment in TS.

Method: A double-blind, randomized, sham-controlled trial was performed in patients with TS over the age of 16 with stable clinical status and medication regimen. 24 participants were recruited (12 treatment, 12 sham; 8 females; median age 26, range 17-61). The intervention involved two 20-minute periods of either sham or 1mA active cathodal tDCS over the SMA per visit day, spanning five days, during which the patients were instructed to employ habit reversal training methods to suppress tics. Evaluations of tic severity were completed at baseline, on day 5 (visit 5), and one week after the final session (visit 6). The primary endpoint was the total tic sub-score of the Yale Global Tic Severity Scale (YGTSS-TTS). Additional measures relating to tics such as the Premonitory Urge for Tics Scale (PUTS) and questionnaires focusing on comorbidities (such ADHD and OCD) were also performed.

Results: There was a significant effect of time on YGTSS-TTS (p<0.0001) but no significant effect of treatment arm (p=0.5951) and no significant time x treatment arm interaction (p=0.0637). Conversely, when motor and phonic sub-scores of the YGTSS-TTS were analyzed separately, there was a significant interaction between time and treatment arm on the motor sub-score of the YGTSS-TTS (p=0.0275) but not the phonic sub-score. Post-hoc comparisons showed a greater reduction in the mean motor sub-score of YGTSS-TTS from visit 1 to visit 6 in the active treatment arm (16.63 [SD 3.60] to 11.29 [SD 2.40]) compared to the sham arm (16.00 [SD 2.92] to 13.29 [SD 3.09]). Additionally, there was a significant time x treatment arm interaction (p=0.0477) on PUTS scores.

Conclusion: This is a proof-of-principle study suggesting that bilateral tDCS over the SMA may help reduce motor tic severity in TS. Future studies with larger sample size are needed to replicate this finding.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/randomized-controlled-trial-of-supplementary-motor-area-transcranial-direct-current-stimulation-in-tourette-syndrome/