Objective: To retrospectively evaluate effect of directional DBS stimulation on ataxia in an essential tremor patient population.

Background: Essential tremor is the most common movement disorder, with most cases rendered medically-refractory within as little as 1 year. Deep brain stimulation (DBS) of the ventral intermediate nucleus of the thalamus (VIM) is approved for essential tremor reduction, but traditional implantation methods and hardware limitations have shown that ataxia can be a common complication, especially with bilateral surgery. This is particularly troublesome given increasing evidence for cerebellar pathology in essential tremor and the commonality of ataxia as a concomitant neurological feature in essential tremor plus. Given evidence that stimulation-induced ataxia can be related to volumes of tissue activation (VTA) which extend too anterior and medial, and given the narrow, columnar shape of the VIM, utilizing segmented DBS electrodes theoretically provides a programming advantage over traditional methods.

Method: A retrospective chart review of documented Scale for Assessment and Rating of Ataxia (SARA) scores were analyzed to determine whether there was a statistically-significant reduction in ataxia scores by directional stimulation as compared to omnidirectional stimulation. A preliminary 5 subjects were reviewed, with intention of following further subjects over the next 6 months in a similar fashion. All subjects underwent bilateral VIM implantation with microelectrode recording; segmented lead position and orientation confirmed via post-operative MRI; and VTA mapping performed via intraoperative stimulation.

Results: To date, total SARA score was significantly reduced by an average of 6.8 points (p = 0.004; 95% CI 1.49-7.16) by steering the VTA away from medial and/or anterior structures surrounding the VIM. Even when removing the tremor subscore from SARA results, a statistically-significant average reduction of 6.4 points was noted via segmented stimulation (p = 0.003; 95% CI 1.31-6.30).

Conclusion: This retrospective analysis appears to show evidence for improved outcomes through directional stimulation in bilateral VIM DBS implantation as related to reduction of ataxic side effects that have traditionally plagued post-operative results, all while providing optimized tremor reduction via stimulation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/reducing-ataxic-side-effects-from-vim-dbs-implantation-in-essential-tremor-advantages-of-directional-stimulation/