Essential Tremor, Movement Disorders

Background and Rationale Essential tremor (ET) affects over 6 million Americans and approximately 5% of adults over age 60. Patients with ET have a 10-20 times higher risk of developing Parkinson's disease (PD) compared to age-matched populations, with approximately 1% converting to PD annually. Post-mortem studies reveal Lewy body pathology in some ET patients, suggesting a subset may have prodromal PD. Current diagnostic tools (DaTscan, SYNTap) are either insufficiently sensitive for early disease, too expensive, or too invasive for routine screening. The Syn-One Test offers a minimally invasive approach to detect phosphorylated α-synuclein (P-SYN) pathology in skin biopsies. Primary Objectives 1. Identify which ET patients have P-SYN pathology indicative of prodromal PD 2. Predict which patients are most likely to phenoconvert to PD

This study aims to recruit patients already implanted with Deep Brain Stimulation (DBS) for movement disorders to complete tasks assessing parameters of motor output, speech, and swallowing functions, both with and without stimulation. DBS parameters would be adjusted prior to motor testing. Patients would then participate in multiple sessions performing contralateral upper extremity movement tasks measuring movement speed, grip strength, and strength modulation, facial movement, swallowing, and speech tasks.

In this study the investigators aim to enroll patients scheduled to undergo deep brain stimulation (DBS) implantation for movement disorders for intra-operative testing. In addition to standard-of-care surgical procedure to implant deep brain stimulation electrode leads, participants will also be stimulated and recorded from cortical areas by a temporary strip electrode (1X6) in the subdural space. The electrodes will be connected to external stimulators and a series of experiments will be performed to assess effects of the DBS on movement quality and electrophysiology measures. Results of this study will elucidate the biological mechanisms related to deep brain stimulation in modulating motor and speech function in patients with abnormal movement disorders.

The goal of this observational study is to evaluate the long-term efficacy and safety of MR-guided focused ultrasound (MRgFUS) thalamotomy in patients with medication-refractory essential tremor. The main questions it aims to answer are: 1. Does MRgFUS thalamotomy provide sustained reduction in tremor severity over 3 years? 2. What are the long-term neurological and quality-of-life outcomes associated with this procedure? Participants will: * Undergo MRgFUS thalamotomy as part of standard of care at Sunnybrook Health Sciences Centre. * Be followed prospectively for a minimum of 3 years with scheduled assessments including: 1. Clinical Rating Scale for Tremor (CRST) 2. Neurological exams and adverse event monitoring 3. Quality of Life in Essential Tremor (QUEST) questionnaire 4. Scale for the Assessment and Rating of Ataxia (SARA) 5. MRI imaging and neuropsychological testing