Improvement in Parkinson disease by subthalamic nucleus stimulation based on electrode placement

Background: The misplacement of electrodes is a possible explanation for suboptimal response to bilateral subthalamic nucleus (STN) stimulation in patients with Parkinson disease. Objective: To evaluate whether reimplantation of electrodes in the STN can produce improvement in patients with poor results from surgery and with suspected electrode misplacement based on imaging findings. Design: Prospective follow-up study. Setting: Academic research. Patients: A 1-year postoperative study was undertaken in 7 consecutive patients with Parkinson disease who, despite bilateral STN stimulation, experienced persistent motor disability and who were operated on for reimplantation a median of 16.9 months later. Main Outcome Measures: The primary outcome was measured as the change in the Unified Parkinson Disease Rating Scale (UPDRS) motor score 1 year after reimplantation. The secondary outcome was measured as the extent of pharmacologic and electrical treatments required and the threshold at which the first stimulation-induced adverse effect appeared. The distances between the electrode contacts used for chronic stimulation and the STN theoretical effective target, defined as the mean position of the clinically efficient contact from 193 previously implanted electrodes, were compared. Results: Except for a single patient, all patients displayed improvement following reimplantation. Under off-medication (ie, the patient is taking no medication) condition, STN stimulation improved the basal state UPDRS motor score by 26.7% before reimplantation and by 59.4% at 1 year after reimplantation. The median off-medication Schwab and England score improved from 51% to 76%. The median levodopa equivalent daily dose was reduced from 1202 mg to 534 mg. The stimulation varibles changed from a mean of 2.6 V/73.0 mu s/163.0 Hz to 2.8 V/60. 0 mu s/140.0 Hz. The mean threshold of the first stimulation-induced adverse effect increased from 2.6 to 4.4 V. The mean distance between the contacts used for chronic stimulation and the theoretical effective target decreased from 5.4 to 2.0 mm. This distance correlated inversely with the percentage improvement in the UPDRS motor score. Conclusion: Patients demonstrating poor response to STN stimulation as a result of electrode misplacement can benefit from reimplantation in the STN closer to the theoretical target.