EP 62. Motor evoked potentials mapping improves detection of capsular side effects during deep brain stimulation

Abstract

Introduction One of the main reasons to perform deep brain stimulation (DBS) on awake patient is detection of activation of descending capsular motor pathways as they represent therapy-limiting side effect. Current technique of capsular activation detection is based on visual detection of muscular contraction during stimulation with standard “tonic” DBS stimulation parameters. Intraoperative mapping of subcortical motor evoked potentials (MEP) during DBS surgery, as already shown in the literature, is feasible and time-efficient, also in patients under general anesthesia. We investigate value of motor evoked potentials mapping in basal ganglia as alternative measurement of safe therapeutic window in stimulation parameters. Methods This study includes recording data of 7 Patients, undergoing awake DBS surgery in subthalamic nucleus or in thalamus and of 1 DBS patient under general anesthesia. Recording data of 16 trajectories and 32 stimulation sites was available. Anodal stimulation was applied in stereotactic target on the macroelectrode tip (microTargeting electrodes, FHC, USA) using train-of-five technique in 1 mA steps 0–5 mA. Recordings were obtained using skin surface electrodes on projection of m. mentalis, m. abductor pollicis brevis, m. flexor digitorum, m. tibialis anterior on contralateral to stimulation side. Visual detection of motor contraction under 130 Hz 60 μs stimulation in 1 mA steps (0–5 mA) was used as standard control parameter. Results MEP recordings were successful in all stimulation sites. MEP threshold current correlated with current values of 130 Hz stimulation, which caused visually detectable muscle contractions and with postoperative DBS side effect thresholds. Detection of muscle response activation was very sensitive and muscle-specific and remained stable under repeated stimulation. Patients described very little or no discomfort during MEP mapping, significantly lower comparing to classical 130 Hz stimulation on motor-threshold. MEP threshold detection was easily obtainable under propofol-remifentanyl general anesthesia and had same current values as “tonic” stimulation postoperatively. Conclusions MEP mapping in basal ganglia is safe and feasible alternative to standard motor side-effect detection, which can improve safety and comfort of DBS procedure. MEP motor threshold correlates well to capsular activation with standard DBS parameters and can be obtained under general anesthesia.