Comparative Study of Focused Ultrasound Unilateral Thalamotomy and Subthalamotomy for Medication-Refractory Parkinson's Disease Tremor

Abstract

Background: Unilateral focused ultrasound ventral intermediate thalamotomy (Vim-FUS) is effective in treating Parkinson's disease (PD) tremor. Ultrasound ablation of the subthalamic nucleus (STN-FUS) has demonstrated efficacy in improving all cardinal motor features of PD, including tremor.

Objective: To compare the efficacy in parkinsonian tremor control between Vim-FUS and STN-FUS.

Methods: Retrospective, two-center study including consecutive PD patients with medication-refractory tremor who underwent unilateral Vim-FUS or STN-FUS between June 2015 and August 2022. Patients scored ≥2 for postural and/or resting tremor on the most affected body side in the off-medication state. The primary outcome was the between-group difference in tremor improvement on the treated side at 12-month follow-up, including a responder's analysis. Data regarding safety, global motor status, and dopaminergic requirements were also collected. Group comparisons used repeated measures ANOVA with Bonferroni correction; statistical significance for P < 0.05.

Results: Among 175 patients treated at the two sites, 63 were included (23 Vim-FUS, 40 STN-FUS). At baseline, both groups were equivalent in disease duration (6.7 ± 3.8 vs. 6.1 ± 3.4 years, P = 0.48) and tremor severity (5.7 ± 1.5 vs. 5.9 ± 2.5, P = 0.7). While the benefit in tremor was equivalent between the groups at 4 months (P = 0.15), tremor reduction was greater in STN- FUS patients at 12 months (4.4 ± 2.0, 95% CI 3.7-5.0 compared with 2.7 ± 3.7, 95% CI 1.1-4.3 for Vim-FUS, P = 0.012). In 47.5% (19/40) of STN-FUS patients tremor was completely abolished versus 8.7% (2/23) in Vim-FUS patients (P < 0.01). Most adverse events were mild (91%) and resolved by 12 months.

Conclusions: STN-FUS and Vim-FUS significantly improved medication-refractory PD tremor; however, subthalamotomy might have greater and more sustained effect. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Keywords: Parkinson' disease; focused ultrasound; subthalamic nucleus; tremor; ventrointermedius nucleus.

FIG. 1

Patient flowchart. PD, Parkinson's disease; STN‐FUS, ablation of the subthalamic nucleus; Vim‐FUS, ablation of the ventral‐intermediate nucleus; GPI, globus pallidus internus; PTT, pallido‐thalamic tract; ET, essential tremor; DBS, deep brain stimulation.

FIG. 2

Effect of focused ultrasound thalamotomy and subthalamotomy on parkinsonian tremor. Shown are the absolute tremor reduction (A), percentage of tremor reduction (B), and the individual responses to ablation of the subthalamic nucleus (STN‐FUS) (C) and ablation of the ventral‐intermediate nucleus (Vim‐FUS) (D) on the treated side of the body at 12 months. Tremor raw scores and percentage of change are assessed according to the Movement Disorder Society‐Unified Parkinson's Disease Rating Scale‐Part III (MDS‐UPDRS‐III) tremor subscore after 12 h of dopaminergic drug withdrawal (off‐state). Both treatments improved tremor significantly but, at 12 months, the benefit of STN‐FUS over tremor was superior to Vim‐FUS, as patients treated with the latter showed a decrease of benefit from 4 to 12 months. (E) shows responder rate distribution at 12 months for both STN‐FUS and Vim‐FUS patients. Responders were defined depending on tremor score at 12 months. Patients scoring 0 were defined as full responders, those scoring 1 as partial responders, those scoring 2 as insufficient responders, and patients with scores of 3 or higher as non‐responders. Data are given as mean ± SE. *P < 0.05. Follow‐up timepoints windows correspond to 4 (±1.5) months and 12 (±1) months after unilateral focused ultrasound ablation. STN‐FUS, ablation of the subthalamic nucleus; Vim‐FUS, ablation of the ventral‐intermediate nucleus; n.s., not significant; t.s., treated side. [Color figure can be viewed at wileyonlinelibrary.com]