Objective: To compare circular, directional and bipolar stimulation in VIM-implanted PD- and ET-patients regarding effect and side-effect thresholds in a cross-sectional design.

Background: So far, little is known about the advantages of directional DBS in VIM-implanted patients. Also the benefit of combining directional with bipolar DBS to raise side-effect thresholds has not been systematically investigated.

Methods: Fourteen patients with VIM-DBS (7 ET, 7 PD) were enrolled in the study. Side-effect thresholds were investigated in the different stimulation-settings focusing on the electrode with the best clinical effect (contralateral to the tremor-dominant side). In a randomized order directional DBS in a monopolar setting (DIRECT) was compared to circular DBS as well as to two bipolar stimulation-settings (BIPOLAR=cathode: active electrode/s, anode: the other segmented level; BIPOLAR-DIRECT=anode and cathode are located on the same segmented electrode-level). To compare the therapeutic effect of each setting patients were stimulated right under the individual side-effect threshold and tremor was measured using the TRS-hemi-score. Side-effect thresholds and therapeutic outcomes were analyzed using Friedman tests with a significance threshold of p < 0.05 and Wilcoxon signed rank tests for post hoc pairwise analysis corrected using the Bonferroni method for multiple comparisons.

Results: Directional DBS showed higher side-effect thresholds compared to circular DBS (p=0.0063). Also side-effect thresholds could be raised by using bipolar stimulation compared to monopolar stimulation (BIPOLAR p=0.0029, BIPOLAR-DIRECT p=0.0022). Side-effect thresholds did not differ between both bipolar settings even though the occurrence of side effects was less under BIPOLAR-DIRECT stimulation (2 patients had side-effect vs. 5 in BIPOLAR). Regarding the therapeutic effect no difference in TRS hemi-scores was found between the three stimulation settings, but all three setting showed significant improvement compared to stimulation-OFF (p < 0.0001).

Conclusions: Directional DBS in VIM-implanted patients as well as bipolar stimulation can raise side-effect thresholds while having an at least equal therapeutic effect. We could not prove that directional bipolar stimulation is able to raise the thresholds even further, but nevertheless it might be considered in single patients with early side-effects.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/bipolar-directional-dbs-in-vim-stimulated-patients/