Objective: To analyse the effects of unilateral magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy defined by 4-tract tractography on axial tremor at 6 months in patients diagnosed of essential tremor (ET).

Background: MRgFUS thalamotomy has been approved by FDA for ET treatment in drug-resistant patients. While beneficial effects of MRgFUS thalamotomy in contralateral-limb tremor are largely recognized, only one study have established the improvement in axial tremor.

Method: We present a prospective quasi-experimental study, uncontrolled before-and-after, of 24 consecutive patients diagnosed of ET and treated with unilateral MRgFUS thalamotomy in our hospital from July 2021 to June 2022. Women represent 62% of the sample, with mean age of 72.13 ± 3.47 years. The target was the ventral intermediate nucleus (VIM), treating left side in 83% of patients.

Each patient was evaluated at baseline and 6 months later. To establish treatment response, the Clinical Rating Scale for Tremor (CRST) was used. Axial tremor improvement was assessed by analysing the axial subscores of the scale. The thalamic VIM target was determined by 4-tract tractography techniques and coordinates were compared with indirect-derived measurements.

Results: Significant improvement at 6 months after MRgFUS thalamotomy was observed in part A subscores evaluating tongue and voice tremors (p<0.05). The decrease in facial and head tremors was not significant. No patient had trunk or orthostatic tremor at baseline score so no changes could be evaluated. In CRST part C, the improvement in speaking and social activities scores also reached statistical significance. Tractography-based coordinates were located more medially than those calculated by indirect-based methods (mean, in mm): ML 13.3±1.5, AP 5.7±1.34, SI 1±1 versus ML 14-15, AP 6.5-8.4, SI 0-2, respectively.

Conclusion: Our study demonstrated a significant improvement in tongue and voice tremor with unilateral tractography-defined MRgFUS thalamotomy. An amelioration in face and head tremor was also observed but the probable effect of a small sample size prevented them to reach statistical significance.

We also noticed that tractographic coordinates determined a more medial target, consistent with the hypothesis that localization of VIM by tractography is beneficial in improving axial symptoms of ET.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/axial-tremor-response-to-tractography-defined-focused-ultrasound-thalamotomy-for-essential-tremor-a-prospective-study/