gms | German Medical Science

Objective: 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.

Method: 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 policis brevis, m. flexor digitorum, m. tibialis anterior on contralateral to stimulation side. Visual detection of motor contraction under 130Hz 60µs 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 130Hz 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 130Hz 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 during DBS is safe and feasible alternative to standard motor side-effect detection, which can improve safety and comfort of awake procedure. MEP motor threshold correlates well to capsular activation with standard DBS parameters and can be obtained under general anesthesia.