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STN and GPi stimulation found equally effective
For many patients with advanced Parkinson's disease, deep brain stimulation can mean the difference between having difficulty walking and being able to run. Since its approval by the Food and Drug Administration in 1997, the treatment has been used by 20,000 patients with advanced Parkinson's disease or other movement disorders to help control their symptoms. Now, researchers have discovered that surgically implanting electrical stimulators on just one side of a patient's brain could help alleviate symptoms on both sides of the body, potentially cutting the surgery risk for some patients. The results are published in the October issue of the journal Motor Control.
There are currently two sites in each hemisphere of the brain where stimulation is targeted. In the same study, researchers found no significant difference in motor performance between two groups of patients who received stimulation at either site. But given past evidence that patients who receive stimulation at one of the sites may be more prone to depression and other neuropsychological conditions, the study's authors conclude the current bias toward placing the implants on that site may be unwarranted.
"These data clearly indicate that unilateral deep brain stimulation improves bilateral motor performance of the arms and hands," said Jay Alberts, an assistant professor in the School of Applied Physiology at the Georgia Institute of Technology.
Alberts, along with researchers from Emory University and the University of Florida, collaborated on a study in which 10 patients with advanced Parkinson's disease participated in a series of tests designed to measure upper body motor performance. The tests were designed to mimic everyday activities that Parkinson's patients often have trouble with, such as opening jars or tying shoelaces. The patients performed the tests while the stimulator was on and then three hours after it was turned off.
Deep brain stimulation works by using electrical impulses to block abnormal nerve signals that cause tremors and other symptoms of Parkinson's. A surgeon implants an electrical lead in either the subthalamic nucleus (STN) or the globus pallidus interna (GPi), two areas of the brain that contribute to movement. The stimulating electrode is connected to a control unit, implanted near the collarbone, that determines how much and how frequently stimulation should occur.
Typically, leads are implanted on the side of the brain opposite to where the effect is needed. So leads placed on the left side of the brain alleviate symptoms on the right side of the body. This is the first study to show the implants significantly improve a patient's symptoms on the same side of the body.
"While on stimulation, patients in both groups improved motor performance of the upper extremity, opposite side of stimulation, by approximately 30 percent," said Alberts. "But when we looked to see if they had any effect on the same side of the body, we found that our patients had experienced about a 14 to 17 percent improvement."
Getting substantial improvements on both sides of the body from just one implant is important, because this is brain surgery, said Michael Okun, Co-director of the Movement Disorders Center at the University of Florida and co-author of the study.
"We may learn from future studies that not everyone requires two devices, and this will cut the risk for some patients in half," he said.
The study also found no significant differences in motor function or force production between patients who had stimulation at the STN or GPi sites, a finding Alberts believes to be equally important as the bilateral effects of stimulation.
"STN stimulation has been touted as the target of choice, but we found GPi stimulation to be equally effective in improving upper extremity motor function," said Alberts. "There is some evidence that there are side effects associated with STN stimulation, such as depression and a decrease in working memory, that haven't been found with GPi. Given that evidence and our latest study, we think the current bias towards STN stimulation needs to be reexamined."
For patients, the effects of the stimulators are life changing. Study participant Joel Moss was diagnosed with Parkinson's disease in 1985. He had his first implant, on the left side of this brain, in 1999. He was not told whether he is receiving STN or GPi stimulation so he can continue to participate in clinical studies.
"The pain went away instantly. The tremors aren't even in existence any more and my balance is good enough to allow me to run," said Moss. "With the stim on you can be close to normal. With it off, you can be close to vegetative."
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