Deep brain stimulation appears to help people with Parkinson’s disease over the long term, according to the first randomised clinical trial to look at its effect on patients’ motor symptoms three years later. The study is published in the 20 June 2012, online issue of Neurology, also brought up the question of which is the correct target for stimulation, the internal globus pallidus or the subthalamic nucleus.
The objective of the study was to compare long-term outcomes of deep brain stimulation of the globus pallidus interna and subthalamic nucleus for patients with Parkinson’s disease in a multicentre randomised controlled trial.
For the study, 159 people with Parkinson’s disease randomly assigned to deep brain stimulation of the globus pallidus interna or subthalamic nucleus of the brain were followed for three years. Participants reported motor symptoms in a diary for 30 minutes every half hour for two days before each of the six study visits. Medication use was allowed in the study. The primary outcome was motor function on stimulation/off medication using the Unified Parkinson’s Disease Rating Scale motor subscale. Secondary outcomes included quality of life and neurocognitive function.
Authors of the study concluded that the beneficial effect of deep brain stimulation on motor function was stable and comparable by target over 36 months. “Slight declines in quality of life following initial gains and gradual decline in neurocognitive function likely reflect underlying disease progression and highlight the importance of nonmotor symptoms in determining quality of life,” they wrote.
While stimulating the subthalamic nucleus has usually been the norm, the new research finds that stimulating the internal globus pallidus may provide some long-term advantages.
“Past studies have had mixed results about which area of the brain benefits the most from deep brain stimulation,” said study author Frances M Weaver, Hines Veterans Administration Hospital and Loyola University Stritch School of Medicine in Maywood, USA. “In our study, deep brain stimulation of both areas improved motor symptoms by 32% on average over the course of three years. However, deep brain stimulation of the globus pallidus interna region of the brain was associated with a slower decline in thinking skills. More research will help us to find out whether medication or the deep brain stimulation was responsible for these differences.”
The study does have one major limitation, according to accompanying editorial author Michele Tagliati, Cedars-Sinai Medical Center in Los Angeles, USA, and a fellow of the American Academy of Neurology. “A fairly large amount, or about 50%, of the initial participants could not be observed at three years due to the original study design and timeline. However, these data provide more reliable evidence that the improvement of motor symptoms of Parkinson’s disease by deep brain stimulation remains stable over the long term regardless of the area in the brain in which the deep brain stimulation occurs,” said Tagliati.