Theta Burst Transcranial Focused Ultrasound as a Novel Treatment for Cervical Dystonia

Patients will be randomly assigned to one of three conditions (n =12 per condition): 1) bilateral tbLIFUS of the GPi, 2) bilateral tbLIFUS of the DN, and 3) bilateral sham tbLIFUS. Study participants will be randomized in a 1:1:1 fashion. In each group, the patients will receive tbLIFUS for five consecutive days. tbLIFUS will consist of two 120 s stimulation (one for each hemisphere, separated by 1 min). Visit 1 will consist of an anatomical MRI scan for each subject to allow accurate targeting of the GPi and DN, and for modelling the ultrasound distribution. Visit 2 will consist of baseline clinical assessments followed by pre-LIFUS rsfMRI. Immediately after, patients will receive tbLIFUS. Visits 3-5 will consist of tbLIFUS only. In Visit 6 (day 5 of stimulation), patients will receive tbLIFUS followed by rsfMRI and clinical assessments. In Visit 7, patients will undergo clinical assessments one week (+/- 3 days) after the last stimulation session in Visit 6. All patients and evaluators will be blinded to the stimulation condition. Visits 2-6 (stimulation days) will be conducted on five consecutive days. Outcome variables will be functional connectivity using rsfMRI, dystonia assessment (TWSTRS and DNMSQuest), cerebellar function assessment (Scale for the Assessment and Rating of Ataxia, SARA), head angle, tremor measurements, and phasic neck movements. SARA will be used in all conditions but will be primarily used to ensure that our protocol does not cause cerebellar dysfunction due to tbLIFUS of the DN. Tremor and phasic neck movements will be quantified with a three-axis accelerometer and neck angle will be measured using a goniometer. All clinical assessments will be video recorded and scored by two blinded movement disorders neurologists.