Objective: To report interim results of an ongoing trial of unilateral transcranial MR-guided high intensity focused ultrasound (tcMRgFUS) ablation of the cerebellothalamic tract (CTT) in essential tremor (ET).

Background: tcMRgFUS allows for the ablation of deep brain structures under direct MR guidance without affecting surrounding tissue. As the main cerebellar afferent to the thalamic ventral intermedius (VIM) nucleus, the CTT is part of the tremor network in ET.

Methods: Prospective, uncontrolled, open-label, blind-assessed, single center interventional study. ET patients fulfilling criteria for interventional neurosurgical therapy received ablation of the CTT using the ExAblate Neuro tcMRgFUS system. Motor symptoms, neuropsychological (MMS, MoCA, TMT A&B) and manual dexterity examination (9-hole peg test (9-HPT) were assessed pre-, 48h and 1,3 & 6 months post intervention. Standardized video-recordings were rated by a physician not involved in the treatment of the participants, and the following tremor sub-scores calculated in keeping with existing literature: overall sum (all items on the Fahn-Tolosa-Marin tremor scale/CRST), speaking & working score (items 15-21). Unilateral hand (items 5,6,11-14) and drawing & pouring (items 11-14) sub-scores were calculated for the treated and non-treated side.

Results: 6 patients (4 f, 4 right-handed) received tcMRgFUS ablation of the CTT contralateral to the mainly affected, treated hand (5 right). Repeated measures ANOVA (Greenhouse-Geisser correction) determined a statistically significant reduction in the following CRST sub-scores (mean score reduction pre-M6 in %): overall sum (F=36.1, p=0.01, 47.8%), speaking & working (F=25.8, p=0.016, 84.7%), unilateral treated hand (F=168.6, p=0.004, 84.3%) and drawing & pouring (F=12.0, p=0.035, 68.3%), while there was no change in the unilateral not treated hand and drawing & pouring sub-scores. 9-HPT (31.5 vs. 30.0), TMT A (49.0 vs. 42.0) TMT B (137.0 vs. 124.7), MMS (28.5 vs. 27.8) and MoCA (25.5 vs. 27.0) scores did not change. Transient side effects (n=3) were subjective ipsilateral hand clumsiness and mild gait instability for a maximum of 3 months.

Conclusions: Unilateral tcMRgFUS lesioning of the CTT was highly efficacious in reducing contralateral hand tremor in ET without affecting manual dexterity. Adverse effects were mild and transient.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/unilateral-mr-guided-high-intensity-focused-ultrasound-ablation-of-the-cerebellothalamic-tract-in-essential-tremor/