Introduction: Asleep, image-guided DBS surgery has become standard at many institutions; however, multiple factors affect accuracy of lead placement. Novel placement of subdural electrocorticographic strips also allows for both the recording of motor evoked potential during surgery and programming of closed-loop protocols. We investigate the modulatory influence of STN DBS stimulation on threshold MEP current necessary to drive EMG response.

Methods: Patients scheduled to undergo STN DBS were consented for participation with intraoperative ECoG strip placement and DBS research protocols and intraoperative recording. The Tucker David Technologies (TDT) 5Z5D bioamp processer was used for STN stimulation and ECoG recording. Median nerve SSEP phase reversal methodology identified electrodes over motor cortex. MEPs were then conducted identifying qualitative minimum current (n) threshold to elicit a resultant EMG response. The effect of DBS for each electrode pair (0-/1+,1-/2+,2-/3+) was tested with DBS off (baseline), stimulation (DBS), and off again (washout). DBS conditions were tested with 5 increasing MEP stimulation amplitudes. All data was analyzed using MATLAB software using maximum recorded EMG response. Statistics were calculated using an estimated EC50 approach as well as an n-way ANOVA.

Results: Five Parkinson’s patients underwent bilateral, asleep, image-guided STN stimulation with left-sided subdural strip placement at our institution. In four of five patients, the most proximal electrode pairs, 2-/3+, showed the largest decrease in MEP threshold, which was significant with either the EC50 based or ANOVA statistical analyses. In one patient, the greatest effect on threshold was seen in the middle, 1-/2+ electrode pair.

Conclusions: Bipolar DBS stimulation produces consistent effects on MEP thresholds, with the superior electrode pairs having a marked modulatory effect in most patients. These results may reflect increased cortical activity with DBS stimulation at a specific anatomic area and may be useful for intraoperative physiological electrode confirmation in asleep settings.

Patient Care: This may approach may improve accuracy of electrode placement during asleep DBS surgery.

Learning Objectives: To investigate the role effect of STN stimulation on MEP.

References: Burchiel KJ, McCartney S, Lee A, Raslan AM. 2013. Accuracy of deep brain stimulation electrode placement using intraoperative computed tomography without microelectrode recording. J Neurosurg 119(2):301-306. Ko AL, Ibrahim A, Magown P, Macallum R, Burchiel KJ. 2017. Factors Affecting Stereotactic Accuracy in Image-Guided Deep Brain Stimulator Electrode Placement. Stereotact Funct Neurosurg 95(5):315-324.