Objective: To describe the phenomenology of dyskinesias induced by subthalamic (STN) stimulation in refractory Tourette syndrome (TS).

Background: Dyskinesias occurring following hemorrhagic events in the STN or direct deep brain stimulation (DBS) of STN for Parkinson’s disease, dystonia or obsessive-compulsive disorders are widely described in literature, underlining the crucial role of STN in a complex network which can generate dyskinesias.

Methods: We conducted a phase II study on efficacy and safety of STN DBS in treating motor and phonic tics in medically refractory TS (ClinicalTrials.gov ID: NCT02619084). One of the secondary objectives of the study was to standardize the best electrical parameters.

Results: Four TS patients (2M/2F) underwent bilateral STN implant (Medtronic 3389 lead, Activa SC pulse generator). Intraoperative microrecording, microstimulation and macrostimulation were performed; correct lead location in the sensorimotor part of STN was verified by postoperative brain CT and MRI scans and 3D neuroatlas reconstruction. In all patients, an important subthalamotomic-like improvement of tic severity was observed, lasting 4.5±2.4 days. In the days and weeks after the clearing of this effect, we performed several sessions of electrical parameters programming. Initial parameters were set as monopolar, 0-3 Volts (0.1 V steps), 125 Hz, 60 µs stimulation, starting with the ventral-most contact. In all patients, a sustained acute tic improvement was observed even following very low stimulation current (average 0,6 ± 0.4 mA). However, slight to severe dyskinesias emerged after brief latency (minutes to several hours), encompassing the full range from dystonic posture to dystonic movements to unsustainable choreic-ballic dyskinesias. Dyskinesias distribution involved mainly the upper limbs, the lower cranial district and the neck and less the lower limbs. Dyskinesias severity correlated directly to current, to subthalamic spreading and to the ventralmost contacts. Slow habituation was observed only for low current stimulation, thus a very narrow therapeutic window was generally found.

Conclusions: Our data suggest a sustained effects of STN DBS in treating tics in refractory TS patients at the cost of dyskinesias risk, and highlight the need to better define the pathophysiology of this crucial node of the cortico-basal ganglia-thalamo-cortical circuitry in organizing fine tuning of motor control.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/phenomenology-of-dyskinesias-induced-by-subthalamic-stimulation-in-tourette-syndrome/