Objective: To test safety and efficacy of inhibitory transcranial direct current stimulation (tDCS) over the supplementary motor area (SMA) for the treatment of tics.

Background: Following sparse anecdotal evidence, a recent randomized, sham-controlled trial of a single session of 1mA cathodal tDCS of SMA has shown acute improvement of tics without associated changes of M1 excitability.

Method: We are conducting a double-blind, randomized sham-controlled trial comparing efficacy and safety of 5 consecutive daily sessions of 1mA tDCS over the SMA in patients with Tourette syndrome (TS), stable medical/behavioural therapy, and age >16 years. 1mA direct current is delivered by a constant-current stimulator while the patient engages in competing response strategies based on habit reversal training. The cathodal electrode is placed 1.8 cm anterior to the location of Cz, as per 10-20 electrode system. Each session consists of two 20’-long periods, during which the cathode position is alternated 0.5 cm right or left of the median sagittal plane, and the anode is placed over the contralateral mastoid. Primary endpoints are the change of the total tic severity score on the Yale Global Tic Severity Scale (YGTSS-TTS) between baseline and: visit 5 (right after the 5th session); visit 6 (7 days after visit 5). Resting state fMRI at baseline and visit 5 is performed in a subgroup of participants.

Results: Our minimal sample size to detect a change of 9 points of the YGTSS-TTS at a 0.05 α level and a 0.2 β level is 24. We present interim findings from the first 12 participants (5 active, 7 sham; 8 males, 4 females; median age 28, range 17-61 years; history of ADHD in 4, OCD in 3, depressive disorder in 3). Improvement of the YGTSS-TTS between visit 5 and baseline was statistically significant in both arms, but greater in patients in the active arm (10.4; p=0.001) than in the sham arm (6.2; p=0.051). Mean YGTSS-TTS difference between visit 6 and baseline was statistically significant in patients in the active arm (11.6; p=0.02), but not in the sham arm (6.2; p=0.14). The treatment was well tolerated by all participants, with one patient in each arm reporting mild, transient headache.

Conclusion: These preliminary results indicate excellent tolerability and promising efficacy of tDCS over the SMA in patients with TS.

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