Objective: To demonstrate the role of contact polarity on therapeutic impedances at two DBS targets.

Background: Neuromodulation with DBS is an established therapy for medically refractory Parkinson’s disease (PD), and essential tremor (ET). Although its clinical efficacy has long been demonstrated, the key parameters to achieve therapeutic stimulation by DBS remain unclear. We hypothesized that therapeutic impedance, an independent measure of circuit configuration, not only varies with each implanted target site but also with therapeutic polarity utilized for optimal stimulation.

Methods: We collected stimulation parameters from the medical records of DBS patients implanted in the Subthalamic Nuclues (STN), and caudal zona incerta (cZi) of ET and tremor predominant PD patients. The stimulation parameters were adjusted for each patient to achieve clinical efficacy of tremor suppression. A longitudinal comparative analysis of the stimulation parameters was performed across the target sites including current/voltage, contact impedance variability, and contact polarity to determine the key parameters contributing to optimal therapeutic impedance over time. A generalized linear mixed model was used to determine if each stimulation parameter had significant effect on therapeutic impedance.

Results: Patients with 18 CZI implanted leads, 14 STN were followed at our tertiary-care movement disorders center with 205 documented visits over a 6month period. Therapeutic impedances in both the STN and cZI reduced over time for monopolar stimulation. However, bipolar configuration, was associated with an increase in therapeutic impedance in cZI. None of the STN leads required bipolar configuration. Active contact impedances, did not change over time between the two targets, regardless of polarity. These findings were independent of disease state. Constant current was a more effective means of stimulating cZI when bipolar activation was used which was the case in 64% of patients by 6 month follow up.

Conclusions: Our findings suggest that STN and cZI targets share similar changes in therapeutic impedances with monopolar stimulation, but an increase is noticeable among cZI patients with bipolar stimulation. Polarity, therefore, may be an important determinant of DBS clinical efficacy in the manner by which stimulation is delivered to a white matter fiber tract (cZI) region.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/role-of-contact-polarity-on-therapeutic-impedances-at-two-deep-brain-stimulation-dbs-targets/