Response to Thalamic Ventralis Intermedius Nucleus Deep Brain Stimulation in Essential Tremor vs. Essential Tremor-Plus.

Gabriela S Gilmour,Zelma H T Kiss,Davide Martino,Karen Hunka,Veronica Bruno,Pia Lawrence

doi:10.3389/fneur.2021.790027

Abstract

Introduction: Essential tremor (ET) is a tremor syndrome characterized by bilateral, upper limb action tremor. Essential tremor-plus (ET-plus) describes ET patients with additional neurologic signs. It is unknown whether there is a difference in response to treatment with ventralis intermedius nucleus deep brain stimulation (VIM DBS) in patients with ET and ET-plus. Due to potential variability in underlying etiology in ET-plus, there is a concern that ET-plus patients may have worse outcomes. The aim of this study was to identify whether patients with ET-plus have worse tremor outcomes after VIM DBS than patients with ET.Methods: This is a retrospective chart and video review evaluating VIM DBS outcomes by comparing changes from baseline in the Fahn-Tolosa-Marin Tremor Rating Scale Part B (FTM-B) for the treated limb between patients with ET and ET-plus at follow-up examinations. Patients were re-classified as having ET or ET-plus using pre-operative examination videos by two independent movement disorders neurologists blinded to patient characteristics. As a secondary outcome, we evaluated for correlations and potential predictors of treatment response.Results: Twenty-six patients were included: 13 with ET, 13 with ET-plus. There were no significant differences in the change in FTM-B scores between the ET and ET-plus patients at each follow-up examination. None of the included patients developed new symptoms compatible with dystonia, parkinsonism or gait disturbances.Conclusions: Patients with ET-plus had tremor improvement from VIM DBS, with no differences when compared to those with ET, without emergence of postoperative neurological issues. Patients with ET-plus should still be considered good candidates for VIM DBS for treatment of tremor.

Highlights

Essential tremor (ET) is a tremor syndrome characterized by bilateral, upper limb action tremor
The primary objective of this study was to identify whether patients with essential tremor-plus (ET-plus) have worse long-term tremor outcomes after ventralis intermedius nucleus deep brain stimulation (VIM deep brain stimulation (DBS)) than patients with ET
ET was defined based on the tremor classification as “isolated tremor syndrome of bilateral upper limb action tremor, at least 3 years’ duration, with or without tremor in other locations, and the absence of other neurological signs, such as dystonia, ataxia or parkinsonism” [3]

Summary

Introduction

Essential tremor (ET) is a tremor syndrome characterized by bilateral, upper limb action tremor. Essential tremor-plus (ET-plus) describes ET patients with additional neurologic signs. It is unknown whether there is a difference in response to treatment with ventralis intermedius nucleus deep brain stimulation (VIM DBS) in patients with ET and ET-plus. In 2018, a new classification for tremor syndromes was introduced which addressed the phenotypic heterogeneity of ET and other tremor syndromes [3] In this classification, patients with tremor consistent with ET, but with additional neurologic signs of uncertain significance such as impaired tandem gait or dystonia, are classified as essential tremor-plus (ET-plus). There exist several invasive treatments, including lesioning or stimulating the ventralis intermedius nucleus (VIM) of the thalamus, effectively reducing upper extremity tremor [8, 9]. There are some risks associated with DBS, which must be considered when determining whether a patient may benefit from it, including paresthesias, headache, gait disorder, dysarthria, stroke, and death [7]

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