Objective: Unilateral focused ultrasound (FUS) thalamotomy of the ventral intermediate thalamic nucleus (FUS-Vim) is effective in treating Parkinson’s disease (PD) tremor. FUS ablation of the subthalamic nucleus (FUS-STN) has demonstrated efficacy to improve all PD cardinal motor features, including tremor. We aimed to compare the efficacy in tremor control between FUS-Vim and FUS-STN in medication refractory Parkinsonian tremor patients.

Background: FUS-Vim may potentially ameliorate pharmacologically refractory tremor in PD patients but the long-term benefit has been questioned.

Method: Retrospective, two-centers study. The analysis included consecutive patients with medication refractory Parkinsonian tremor who underwent unilateral FUS-Vim or FUS-STN. PD patients were included if presenting a score ≥2 for postural and/or resting tremor on the most affected (to be treated) body side in the medication off. The primary outcome was the difference in tremor improvement on the treated side according to the MDS-UPDRS-III throughout 12-months follow-up. Data regarding global motor status, rigidity and bradykinesia, levodopa equivalent daily dose and adverse events were also collected.

Results: Sixty-three PD patients were included (23 FUS-Vim, 40 FUS-STN). At baseline, both groups were equivalent in tremor severity (5.7±1.5 vs 5.9±2.5). Four and 12 months after treatment both groups presented significant improvement in tremor on the treated side (p<0.001 at both time points compared to baseline). Whereas the benefit between groups was equivalent at 4-month, FUS-Vim improved tremor to a lesser extent than FUS-STN at 12 months (mean change 35.2±52.1% vs 76.1±31.6%, p<0.001).

Bradykinesia (t.s.), motor symptoms (t.s) and MDS-UPDRS III were significantly more reduced by FUS-STN compared to FUS-Vim.

Weight gain and dyskinesias were more frequent after FUS-STN, whereas dysgeusia, perioral, and finger paresthesias only occurred after FUS-Vim. Most adverse events were mild and had resolved by 12 months in both groups.

Conclusion: In medication refractory Parkinsonian tremor patients, FUS-STN provided more sustained tremor control and a better effect on bradykinesia than FUS-Vim. Adverse events between targets differed in nature but were mostly mild and transient. Whether STN-FUS is preferable to Vim-FUS for treating severe tremor in PD should be analyzed prospectively.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-comparative-study-of-focused-ultrasound-unilateral-thalamotomy-and-subthalamotomy-for-medication-refractory-parkinsonian-tremor/