Reducing Ataxic Side Effects from Ventral Intermediate Nucleus of the Thalamus Deep Brain Stimulation Implantation in Essential Tremor: Potential Advantages of Directional Stimulation

Objective: The aim of the study was to retrospectively evaluate the effect of directional deep brain stimulation (DBS) on ataxia in an essential tremor patient population.

Materials and methods: A retrospective chart review of documented Scale for Assessment and Rating of Ataxia (SARA) scores were analyzed using a case-control design. All subjects we evaluated were treated at a single, tertiary care academic center. We reviewed 14 patients who underwent bilateral ventral intermediate nucleus of the thalamus (VIM) implantation with microelectrode recording, with electrodeposition and segmented contact orientation confirmed via postoperative computed tomography. The main outcome was to determine change in ataxia scores between directional versus monopolar circumferential stimulation.

Results: Fourteen patients (9 males, median age at implantation 69 [range 63-82]) underwent surgery between October 2017 and July 2020 at the UNC Movement Disorders Center. SARA scores between directional stimulation and monopolar circumferential stimulation demonstrated a significant reduction in total scores with best possible segmented stimulation (n = 13, p < 0.0001, 95% confidence interval [CI] -3.496 to -6.789). This difference remained statistically significant even after removing the SARA tremor subscore (n = 13, p < 0.0001, 95% CI -3.155 to -6.274). In line with prior reports, SARA score changes from the preoperative state were generally worsened when applying monopolar circumferential stimulation bilaterally (n = 13, p = 0.655; 95% CI -2.836 to 4.359), but improved with directional stimulation (n = 13, p = 0.010; 95% CI -1.216 to -7.547).

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