Effects of deep brain stimulation in the subthalamic nucleus or globus pallidus internus on step initiation in Parkinson disease.
Journal of Neurosurgery
Rocchi L, Carlson-Kuhta P, Chiari L, Burchiel KJ, Hogarth P, Horak FB. Effects of deep brain stimulation in the subthalamic nucleus or globus pallidus internus on step initiation in Parkinson disease. Journal of Neurosurgery, 2012 Dec;117(6):1141-9. doi: 10.3171/2012.8.JNS112006. Epub 2012 Oct 5.
Intro: One of the motor complications with PD is difficulty in starting or initiating steps while walking. Although walking may seem simple and easy to most adults, there is a myriad of complex neural connections and multiple motor pathways that are involved in taking a simple step. The literature shows that levodopa usage can help with this difficulty but it is less clear if DBS provides similar benefit.
Methods: Twenty-nine patients with PD that underwent DBS (14 GPi, 15 STN) were studied as were 28 healthy age matched volunteers (control group) and nine individuals with PD that did not undergo DBS. General ages of the groups were 60-62 and the DBS groups were mostly males that had been diagnosed with PD approximately 11-12 years prior to surgery. The surgeries were completed by the same Neurosurgeon and all patients were followed by Neurology for stimulator settings and medication dosages for optimal symptom control. Each of the DBS groups was tested before surgery, on and off their medications, as well as 6 months post surgery, on/off medication and on/off stimulator. Testing consisted of participants standing on and taking steps from flat plates designed to record multiple measurements related to stepping/walking (e.g. pressure, position, velocity/speed, step length, etc.)
Findings: The control group had less difficulty initiating steps compared to the PWP in all medication and stimulator settings, which was an expected finding. However, the authors found that when PWP were evaluated before surgery while taking levodopa there were improved effects on multiple measures such as adjusting ones’ posture in anticipation of taking and shortened amount of time planning to take a step. These findings did not persist after either the DBS STN or GPi surgery for the PWP. The authors also looked at length and speed of taking a step and found that the PWP had slower and shorter steps than the control group. The study again found improvement from taking levodopa in the length and speed of taking a step before the surgery and this result remained in the stimulator on/medication on condition after surgery. However when looking specifically at DBS STN vs. DBS GPi they found that the speed of taking a step while taking levodopa after surgery when the stimulator was on was slower in the STN group. When the authors looked at step initiation in the PWP that did not undergo DBS, they found that this group did better than either of the DBS groups both before and after surgery on the stepping measures. It should also be noted that both the DBS STN and GPi groups showed improvement in overall motor symptoms after the surgery.
Conclusion: This study showed some differing findings of what DBS versus levodopa can do to step initiation in PWP after 6 months of stimulation. It showed that step initiation improved with levodopa prior to surgery but worsened after DBS. Additionally the levodopa response disappeared after surgery. An important point to note about this study is the usage the control group without PD. Comparing the PWP that did not undergo DBS to those that did indicated that the finding of worsened step initiation was not due to disease progression as the non-DBS group did better after a 6 month follow up than the DBS groups. Although many studies have shown improvement in many motor symptoms after DBS surgery, this study is important to show that it may also have an adverse event of worsening gait, specifically hesitating when starting to walk and freezing. More research was recommended using the pre and post designs as well as the control groups to continue to understand the positive and negative implications of DBS for PWP.