Objective: To determine whether directional stimulation of the VIM is superior to omnidirectional stimulation in essential tremor.

Background: Deep brain stimulation (DBS) of the VIM is a well-established therapy in the management of essential tremor but is frequently associated with side effects like gait ataxia. Directional current steering may be a way to activate fiber tracts more selectively, thereby widening the therapeutic window.

Method: For this prospective, randomized, double blind study 10 patients with ET (5 men, 5 women) treated with chronic deep brain stimulation (DBS) of the ventral intermediate thalamic nucleus (VIM) were recruited. To compare efficacy of current steering in VIM-DBS, therapeutic window was calculated under directional (3 directions) and omnidirectional stimulation by determining effect and adverse effect thresholds. Clinical efficacy was assessed by comparing impact of directional and omnidirectional stimulation settings on tremor rating scales (TRS, TETRAS), ataxia rating scales (mICARS, SARA) and accelerometry (Kinesia©). Total electrical energy delivered (TEED) was measured under both conditions.

Results: Therapeutic window under best directional stimulation tended to be wider than under omnidirectional stimulation. This resulted from a significantly lower effect threshold under best directional stimulation compared to omnidirectional stimulation, while there was no difference in terms of adverse effects. Best and second-best directional stimulation had a significantly wider therapeutic window than the third-best directional stimulation. In terms of clinical efficacy, we did not find significant differences. TEED at the adverse effect threshold was significantly higher under directional than under omnidirectional stimulation.

Conclusion: Directional stimulation is at least equally effective, compared to omnidirectional stimulation. Regarding effect threshold, our data even suggest a superiority of directional stimulation settings. Moreover, superiority of certain directions of stimulation may indicate a directional stimulation to be advantageous in case a DBS lead is not optimally placed. Under directional stimulation higher energy levels are needed to evoke adverse effects than under omnidirectional stimulation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/is-directional-stimulation-of-the-vim-superior-to-omnidirectional-stimulation-in-patients-with-essential-tremor/