Intraoperative Microstimulation Predicts Outcome of Postoperative Macrostimulation in Subthalamic Nucleus Deep Brain Stimulation for Parkinson's Disease

Background: In deep brain stimulation (DBS) of the subthalamic nucleus for treatment of Parkinson's Disease, a commonly encountered stimulation side effect is involuntary muscle contractions from spread of electrical current to cortico-spinal and cortico-bulbar fibers in the internal capsule. During surgery, a variety of techniques, including microelectrode recording (MER), are used to avoid positioning the DBS electrode too close to the internal capsule. At some centers, MER includes stimulating through the microelectrode (microstimulation). Objective: To assess if intraoperative microstimulation can help avoid positioning the DBS electrode too close to the internal capsule. Materials and Methods: From clinical records, we compiled microelectrode and DBS-electrode locations, microstimulation effect thresholds and DBS side effect thresholds. Results: We found that capsular macrostimulation thresholds were significantly lower in cases where capsular microstimulation effects were observed. In addition, we found that lower-threshold for microstimulation-induced involuntary muscle contractions from a given DBS electrode contact predicts a lower threshold for involuntary muscle contractions as a side effect of stimulation with that contact. Specifically, our results suggest that capsular macrostimulation thresholds below 2V are avoided when the product of microstimulation threshold (in µA) and distance (in mm) is greater than 500. Conclusions: intraoperative microstimulation can help avoid positioning the DBS electrode too close to the internal capsule.