Deep Brain Stimulation: When to Test Directional?

Abstract

Background: Directional deep brain stimulation (DBS) allows for steering of the stimulation field, but extensive and time-consuming testing of all segmented contacts is necessary to identify the possible benefit of steering. It is therefore important to determine under which circumstances directional current steering is advantageous.

Methods: Fifty two Parkinson's disease patients implanted in the STN with a directional DBS system underwent a standardized monopolar programming session 5 to 9 months after implantation. Individual contacts were tested for a potential advantage of directional stimulation. Results were used to build a prediction model for the selection of ring levels that would benefit from directional stimulation.

Results: On average, there was no significant difference in therapeutic window between ring-level contact and best directional contact. However, according to our standardized protocol, 35% of the contacts and 66% of patients had a larger therapeutic window under directional stimulation compared to ring-mode. The segmented contacts warranting directional current steering could be predicted with a sensitivity of 79% and a specificity of 57%.

Conclusion: To reduce time required for DBS programming, we recommend additional directional contact testing initially only on ring-level contacts with a therapeutic window of less than 2.0 mA.

Keywords: Parkinson's disease; current steering; deep brain stimulation; directional electrodes; subthalamic nucleus.

FIG 1

Differences in the therapeutic window between ring level and corresponding directional contacts. Each point corresponds to the test results of a single contact. Matching box plots and distributions are shown to the left and right of the data points. The shaded area highlights all the contacts that are labeled as “warranting investigation”. P‐values result from the mixed‐effects model described in the Methods.

FIG 2

Effect thresholds, side‐effect thresholds and therapeutic windows from the 153 ring level monopolar reviews. Contacts are labeled as “warranting investigation” if there was a relevant increase of the directional therapeutic window compared to the corresponding ring level.

FIG 3

A: ROC curves showing sensitivity and specificity for varying thresholds for different variables (effect threshold, side‐effect threshold, therapeutic window and the combination of therapeutic window and effect threshold). Shaded areas indicate 95% confidence intervals. B: Predictive performance for effect threshold, side‐effect threshold, therapeutic window and the combination of therapeutic window and effect threshold from the 5‐fold cross‐validation.