Objective: The goal of this study was to study the outcomes of 10 patients with medically refractory Essential Tremor (ET) treated with staged bilateral MR-guided high-intensity focused ultrasound (MRgHIFU) thalamotomy using four tract tractography.

Background: In patients with medically refractory ET, staged, bilateral MRgHIFU thalamotomy improves bilateral tremor control. However, the use of indirect targeting methods can produce unwanted adverse effects. An increased risk of transient gait impairment, motor neglect, ataxia, dysarthria, dysphagia, dysesthesia, and dizziness were noted in the clinical trial studying bilateral MRgHIFU for ET (1). Meanwhile, the use of four tract tractography to target the decussating and non-decussating dentato-rubro-thalamic tracts (DRTT) provides increased patient-specific precision and can improve treatment responses, while reducing adverse effects and treatment times.

Method: Four tract tractography was performed in BrainLab to target the DRTTs while avoiding the corticospinal and medial lemniscus tracts. Patients with bilateral tremor and a history of unilateral MRgHIFU thalamotomy using four tract tractography were recruited for a second procedure. The improvement in tremor response and adverse effects were assessed immediately after MRgHIFU, and at the follow-up visits at 2 days, 1 and 3 months.

Results: Recruitment and treatment ongoing. At this stage, 3 patients have been treated and 12 additional patients have been given treatment dates. At the 1-month clinic visit, all 3 patients had a significant, sustained reduction of the bilateral tremor and substantial voice tremor and axial tremor reduction. This improvement was sustained at the 3-month visit for two of the patients, while this time point has not been reached yet for the other one. In terms of side effects, the 1st patient complained of subjective imbalance at 48 hours, which resolved after a month. The 2nd and 3rd patient did not report any adverse effects. We will report the change in appendicular, axial, and vocal tremor as well as the adverse effects in the 10 treated patients using the TETRAS rating scale.

Conclusion: Bilateral MRgHIFU thalamotomy represents a powerful option for patients with medically refractory ET. The use of four tract tractography for targeting can significantly improve the MRgHIFU outcomes of these patients and reduce adverse effects.

References: 1. Iorio-Morin C, Yamamoto K, Sarica C, et al. Bilateral Focused Ultrasound Thalamotomy for Essential Tremor (BEST-FUS Phase 2 Trial). Mov Disord Off J Mov Disord Soc. 2021;36(11):2653-2662. doi:10.1002/mds.28716

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MDS Abstracts - https://www.mdsabstracts.org/abstract/outcomes-of-patients-treated-with-staged-bilateral-mrghifu-thalamotomy-using-four-tract-tractography-targeting-for-medically-refractory-essential-tremor/