Background and Purpose: For individuals with advanced Parkinson disease (PD), stimulation of the subthalamic nucleus (STN) reduces tremor, rigidity, and bradykinesia, but the effects of stimulation on gait and mobility are not fully understood. The purpose of this paper is to describe the effects of unilateral and bilateral STN stimulation on gait following staged stimulator implantations in a series of individuals with PD. Case Descriptions: Participants were 6 individuals with PD who underwent staged stimulator implantation surgeries. The effects of stimulation on gait were assessed in the optimally medicated state using items from the Unified Parkinson's Disease Rating Scale (UPDRS) related to gait and self-reported mobility, time to complete the Timed Up and Go (TUG) test, and quantitative gait analysis. Gait was evaluated with stimulation turned off and with stimulation turned on after unilateral stimulator implantation and again after implantation of the second stimulator. Outcomes: Variable effects of unilateral and bilateral STN stimulation on gait were observed on UPDRS self-reported mobility, TUG time, and gait velocity, but changes were not detected using the UPDRS gait item. Minimal gait changes, either positive or negative, were detected with unilateral stimulation. With bilateral stimulation, gait improved for 3 individuals but worsened for the other 3 individuals. Discussion: The ability to detect changes in gait after STN stimulation using the UPDRS gait item was limited, but variable effects were detected by self-report, TUG time, and gait velocity. For half of the individuals studied, bilateral stimulation improved these measures, but gait worsened for the remaining individuals. Future research is needed to better understand factors that influence the effect of STN stimulation on walking, and assessment of gait changes in people with PD should include self-report and performance-based measures, such as the TUG test or gait velocity.

Key Words: walking, mobility, deep brain stimulation, Timed Up and Go test, quantitative gait analysis

INTRODUCTION

In the last decade, high frequency stimulation of the subthalamic nucleus (STN) has emerged as an effective treatment for advanced Parkinson disease (PD). During the medication-off state, clinical rating scales show that STN stimulation improves most motor symptoms of PD, including tremor, bradykinesia, rigidity, postural instability, and gait.1-10 Stimulation improves motor function to a lesser extent in the medication-on state, during which the benefits of STN stimulation on speech, postural instability, and gait are less consistent.2-5

Studies using quantitative gait analysis confirm that STN stimulation improves gait in the medication-off state, but the effects in the medication-on state are less clear. In the medication-off state, unilateral STN stimulation improves gait velocity and stride length compared to both the off-stimulation condition11,12 and presurgical values.11 In the medication-on state, however, gait velocity and stride length decrease slightly with unilateral stimulation compared to presurgical values.11 Similarly, bilateral STN stimulation consistently improves gait in the medication-off state, but in the medication-on state, the reported effects on gait are mixed.13-17

Reasons for the variable effects of STN stimulation on walking in the medication-on condition are not well understood. The effects of STN stimulation on gait have been previously evaluated using a variety of measures,5,7,13-17 and the mixed results that are observed in the medication-on condition may be due in part to the different measures used to quantify gait changes. Individual attributes, such as age, duration of disease, presurgical gait function, or presurgical response to anti-parkinson medications, may also contribute to the variable effects of STN stimulation on walking. Variations in how stimulators are programmed could influence how gait responds to STN stimulation. Finally, differences in the utilization of postoperative rehabilitation services could impact gait and mobility outcomes after surgery.

While the factors influencing gait response to STN stimulation are not well understood, the consequences of gait and mobility problems in people with PD are clear. The ramifications of impaired mobility for people with PD include reduced quality of life, decreased independence, and an increased risk of falls and fall-related injuries.18-20 Furthermore, individuals with PD identify walking and mobility limitations as among the worst aspects of the disease.21

Because of their specialized training and expertise, physical therapists are often asked to evaluate changes in gait and mobility in response to surgery or other therapeutic interventions. Accurate assessment of gait and mobility outcomes in response to STN stimulation and a better understanding of the factors that affect these outcomes are critical to our understanding of the impact of this therapeutic intervention. An improved appreciation of how and why gait changes in response to STN stimulation can be used to improve the selection of appropriate candidates for this surgical intervention and to predict individuals who may benefit from postsurgical rehabilitation for gait and mobility. The purpose of this case series report is to describe gait outcomes in response to STN stimulation in the optimally medicated state after each of two staged stimulator implant