Neuroanatomical Correlates of Response to Focused Ultrasound Thalamotomy in Essential Tremor

Abstract

Abstract INTRODUCTION Essential tremor (ET) is the most common movement disorder. While for the majority of patients medical management has shown to decrease tremor by more than 60%, disabling tremor persists in a significant subset of this population. Recently, MR-guided focused ultrasound (MRgFUS), a non-invasive means to ablate biological tissue, has proven to be a minimally invasive, effective treatment option to achieve thalamotomy. METHODS Sixty-eight patients (mean age 72.6 yr, 72% male) diagnosed with ET undergoing MRgFUS thalamotomy between 2012 and 2018 were included for analysis. Baseline ipsilateral hand and axial tremor scores were compared to 3-mo post-treatment scores. Clinically weighted probabilistic maps were generated to localize areas associated with improvement and decline in ipsilateral hand as well as axial symptoms. White matter tracts and functional connectivity related to these areas were interrogated. RESULTS The probability maps corresponding to the axial or ipsilateral hand tremor improvement phenotypes were similar, occupying a space near the posterior border of the VIM nucleus, at the boundary of the VIM and VC nuclei. The probability map corresponding to worsening of ipsilateral hand tremor was also infringed the posterior border of the VIM nucleus, although relatively medial compared to the improvement-associated maps. The probability map corresponding to axial decline was located more posteriorly relative to the other 3 maps, sharing no overlap with VIM. Compared to our previously published optimal zone for contralateral hand tremor improvement, areas associated with axial or ipsilateral hand tremor abatement demonstrated 53% and 10% overlap with this zone, respectively. In terms of functional connectivity, activity in the dentate nucleus was more closely associated with ipsilateral hand and axial improvement than with decline phenotypes. The decline phenotypes showed greater association with the motor cortex. CONCLUSION These findings can be used to improve ipsilateral hand and axial tremor symptomatology in ET by honing neuromodulatory and neuroablative treatment strategies.