Improvement in Parkinson Disease by Subthalamic Nucleus Stimulation Based on Electrode Placement

Abstract

Bilateral chronic stimulation of the subthalamic nucleus (STN) is effective in reducing the levodopa equivalent daily dose (LEDD), off-medication (ie, the patient is taking no medication) motor symptoms, levodopa-induced dyskinesia, and motor fluctuations in patients with severe Parkinson disease (PD).^1-7 The Unified Parkinson Disease Rating Scale (UPDRS) motor score during the off-medication period is generally improved by 40% to 70%.^5,7-11 Moreover, the mean LEDD is reduced after surgery by 50% to 65%.¹² However, improvement following surgery can sometimes be less effective, and failure can be suspected of surgery when (1) any improvement from STN stimulation remains far less than the preoperative levodopa response, reported as the best predictive factor for surgery-induced benefit^11,13; (2) the postoperative decrease in the LEDD is minimal⁷; or (3) the initially induced adverse effects occur at lower voltage thresholds, thereby preventing the use of sufficient electrical voltages to improve the motor score. The principal cause of these poor results arises from imprecision of electrode placement, leading to nonstimulation of the target as required.