In addition to the well-recognized ventral intermediate nucleus (Vim) thalamotomy for the treatment of chronic therapy-resistant essential tremor (ET), an alternative approach targeting the posterior part of the subthalamus was proposed in the 1960s and early 1970s and then was reactualized as cerebellothalamic tractotomy (CTT) with the advent of MR-guided focused ultrasound (MRgFUS) surgery. The goal of this study was to improve target coverage and thus efficacy (i.e., tremor control and its consistency). The authors undertook a histological reappraisal of the CTT target and proposed a targeting strategy of the MRgFUS CTT based on 1) the MR visualization of the center of the red nucleus and 2) the application of preplanned target subunits realized with short sonications under thermal dose control. This study was aimed at demonstrating the efficacy and risk profile of this approach against chronic therapy-resistant ET.
Ten consecutive patients suffering from chronic therapy-resistant ET benefited from a unilateral MRgFUS CTT and were followed over the course of 1 year. Primary endpoints were subjective tremor relief, Clinical Rating Scale for Tremor (CRST) score, activities of daily living (ADL) score, and the hand function (HF) scores HF16 and HF32. Histological reappraisal of the target led the authors to propose a standardized targeting protocol for MRgFUS CTT. Thermal doses for 18 and 240 cumulative equivalent minutes at 43°C were calculated and correlated with intraoperative and 2 days postoperative T2-weighted MR images.
The mean ± SD for the baseline CRST score was 48 ± 12; the score was 16 ± 7 at 3 months, and 17 ± 8 at 1 year. The mean tremor relief rated by the patients for the operated side was 95% after 2 days, 96% at 3 months, and 93% at 1 year. The mean HF16 was 11.0 ± 2.1 at baseline, 0.7 ± 0.7 at 3 months, and 0.8 ± 0.9 at 1 year (93% mean reduction). The minimum reduction for the HF16 at 1 year was 78%. There was a 51% reduction of the mean ADL score at 1 year. There was no bleeding or infection. Gait difficulties, only detectable on tandem gait, were increased in 3 patients and reduced in 2 patients at 1 year. There was no dysarthria.
The authors’ results suggest that MRgFUS CTT is a very effective treatment option for therapy-resistant ET.
ABBREVIATIONSADL = activities of daily living; CEM = cumulative equivalent minutes; CLT = central lateral thalamotomy; CMT = centrum medianum thalamotomy; CRST = Clinical Rating Scale for Tremor; CTT = cerebellothalamic tractotomy; ET = essential tremor; HADS = Hospital Anxiety and Depression Scale; HF = hand function; ICP = intercommissural plane; MoCA = Montreal Cognitive Assessment; MRgFUS = MR-guided focused ultrasound; mRN = center of the red nucleus; mtt = mammillothalamic tract; PD = Parkinson disease; STN = subthalamic nucleus; Vim = ventral intermediate nucleus; VLp = posterior part of the thalamic ventral lateral nucleus; VPMpc = ventral posterior medial nucleus, parvocellular division; WHOQOL-BREF = World Health Organization Quality of Life questionnaire.
Correspondence Marc N. Gallay: Center for Ultrasound Functional Neurosurgery, Solothurn, Switzerland. email@example.com.INCLUDE WHEN CITING Published online February 7, 2020; DOI: 10.3171/2019.12.JNS192219.Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.