Safety and Efficacy of Staged, Bilateral Focused Ultrasound Thalamotomy in Essential Tremor: An Open-Label Clinical Trial

Abstract

Importance: Unilateral magnetic resonance-guided focused ultrasound ablation of ventralis intermedius nucleus of the thalamus for essential tremor reduces tremor on 1 side, but untreated contralateral or midline symptoms remain limiting for some patients. Historically, bilateral lesioning produced unacceptable risks and was supplanted by deep brain stimulation; increasing acceptance of unilateral focused ultrasound lesioning has led to interest in a bilateral option.

Objective: To evaluate the safety and efficacy of staged, bilateral focused ultrasound thalamotomy.

Design, setting, and participants: This prospective, open-label, multicenter trial treated patients with essential tremor from July 2020 to October 2021, with a 12-month follow-up, at 7 US academic medical centers. Of 62 enrolled patients who had undergone unilateral focused ultrasound thalamotomy at least 9 months prior to enrollment, 11 were excluded and 51 were treated. Eligibility criteria included patient age (22 years and older), medication refractory, tremor severity (Clinical Rating Scale for Tremor [CRST] part A score ≥2 for postural or kinetic tremor), and functional disability (CRST part C score ≥2 in any category).

Intervention: A focused ultrasound system interfaced with magnetic resonance imaging allowed real-time alignment of thermography maps with anatomy. Subthreshold sonications allowed target interrogation for efficacy and off-target effects before creating an ablation.

Main outcomes and measures: Tremor/motor score (CRST parts A and B) at 3 months for the treated side after treatment was the primary outcome measure, and secondary assessments for efficacy and safety continued to 12 months.

Results: The mean (SD) population age was 73 (13.9) years, and 44 participants (86.3%) were male. The mean (SD) tremor/motor score improved from 17.4 (5.4; 95% CI, 15.9-18.9) to 6.4 (5.3; 95% CI, 4.9 to 7.9) at 3 months (66% improvement in CRST parts A and B scores; 95% CI, 59.8-72.2; P < .001). There was significant improvement in mean (SD) postural tremor (from 2.5 [0.8]; 95% CI, 2.3 to 2.7 to 0.6 [0.9]; 95% CI, 0.3 to 0.8; P < .001) and mean (SD) disability score (from 10.3 [4.7]; 95% CI, 9.0-11.6 to 2.2 [2.8]; 95% CI, 1.4-2.9; P < .001). Twelve participants developed mild (study-defined) ataxia, which persisted in 6 participants at 12 months. Adverse events (159 of 188 [85%] mild, 25 of 188 [13%] moderate, and 1 severe urinary tract infection) reported most commonly included numbness/tingling (n = 17 total; n = 8 at 12 months), dysarthria (n = 15 total; n = 7 at 12 months), ataxia (n = 12 total; n = 6 at 12 months), unsteadiness/imbalance (n = 10 total; n = 0 at 12 months), and taste disturbance (n = 7 total; n = 3 at 12 months). Speech difficulty, including phonation, articulation, and dysphagia, were generally mild (rated as not clinically significant, no participants with worsening in all 3 measures) and transient.

Conclusions and relevance: Staged, bilateral focused ultrasound thalamotomy significantly reduced tremor severity and functional disability scores. Adverse events for speech, swallowing, and ataxia were mostly mild and transient.

Trial registration: ClinicalTrials.gov Identifier NCT04112381.

Figure 1.. Flowchart of Study Recruitment

CRST indicates Clinical Rating Scale for Tremor.

Figure 2.. Tremor/Motor Scores, Postural Tremor Scores, and Tremor Disability Scores at Baseline and Follow-up After Staged Bilateral Focused Ultrasound Ablation

The number of participants assessed at baseline, month 3, month 6, and month 12 visits are 51, 50, 50, and 45, respectively.

Figure 3.. Head and Voice Tremor Scores at Baseline and Follow-Up After Staged Bilateral Focused Ultrasound Ablation

The number of participants assessed at baseline, month 3, month 6, and month 12 visits are 17, 17, 17, and 16 for head tremor and 12, 12, 12, and 11 for voice tremor, respectively.