But coupling the technique known as cortical stimulation with aggressive rehabilitation is key to reversing the impairment, doctors say.
"It's the coolest thing in stroke I've seen in a long time," said Helmi Lutsep, M.D., associate professor of neurology and associate director of the Oregon Stroke Center, OHSU School of Medicine.
In a study examining the safety of cortical stimulation therapy, Lutsep and co-investigators found that stroke patients who received stimulation with rehabilitation improved "significantly" better in hand mobility and strength tests than people undergoing rehabilitation alone.
"Everybody improved to some degree, because even in the subjects who received some rehabilitation, we did see improvement," Lutsep said. "What the data suggested is those who received the (stimulation) implant improved more."
The study was published this month in the journal Neurosurgery. Lutsep's co-investigators were Jeffrey A. Brown, M.D., of Wayne State University, Detroit, Martin Weinand, M.D., of the University of Arizona, Tucson, and Steven C. Cramer, M.D., of the University of California, Irvine.
Ischemic stroke occurs when a clot in a blood vessel blocks the flow of oxygen-rich blood to the brain. The result can be major weakness on one side of the body, a condition called hemiparesis, which is typically treated with rehabilitation. According to the American Stroke Association, 88 percent of the estimated 700,000 strokes that occur each year are ischemic.
In cortical stimulation, a pacemaker-like device called an external pulse generator sends a low current through a wire to an electrode placed surgically atop the dura, the fibrous membrane covering the brain. The electrode rests above the motor cortex, the area in the brain corresponding to hand function. Surgeons pinpoint the site using "neuronavigation" techniques, including functional magnetic resonance imaging, or fMRI, then remove a circular, 4-centimeter flap of the skull to access the dura.
The technique is similar to one used to treat Parkinson's disease called deep brain stimulation, or DBS, which uses electrical impulses sent to two electrodes surgically implanted in the brain to block the signials that cause the disabling motor symptoms of the disease.
"It's like DBS, except that we don't go deep into the brain," Lutsep emphasized. "It's considered generally safer, less invasive, but on the other hand, we still have to go into the skull to place it."
Eight individuals ages 33 to 74 completed the Neurosurgery study. Each had suffered motor deficits resulting from a stroke that occurred at least four months before, and was randomly placed into one of two groups: An active treatment group that received cortical stimulation with three weeks of rehabilitation, and a control group that received rehabilitation alone. In the active treatment group, the device was turned on only during rehabilitation sessions.
The study found that patients in the active treatment group "improved to a significantly greater degree" than control patients, and they continued to improve through the three-week treatment period and into a fourth week, when a follow-up assessment takes place. Active treatment patients even maintained their improvements through the 16th week of the study. In comparison, control patients experienced "lesser" improvements within the study's first two weeks, and the improvements decreased over time.
Researchers believe cortical stimulation induces neurons to rewire themselves in response to the damage caused by stroke, a phenomenon known as plasticity, and rehabilitation continues to encourage this rewiring activity. "The idea is you induce plasticity in the brain and once it's there, you can remove the hardware," Lutsep said.
One study participant, June Wallace, 77, of Portland, said stimulation therapy helped her regain use of her right hand, which has remained weak since suffering a stroke in May 2002.
"Before the study, I had been through just regular rehab and was in the process of trying to shift everything I did to my left side. My right side was pretty useless at that point," she recalled. "Since the study, I can pretty well do everything I did. It wasn't immediate. It was just something that happened. One day, it was like, 'Oh wow! Look what I can do!'"
OHSU is one of 16 sites around the country participating in a follow-up study called EVEREST that will examine a larger group of stroke survivors - 174 people - to confirm the safety and effectiveness of cortical stimulation therapy shown in the Neurosurgery study. Like that trial, the EVEREST trial will focus on people age 21 years and older who have had an ischemic stroke at least four months prior to screening and suffered weakness in one hand or arm.
Stroke patients who would like more information or to enroll in the EVEREST trial should contact the study call center at 888 546-9779.
Portland resident Celeste Thornes, 51, who has had weakness on her left side since suffering a stroke in 1987, has applied for enrollment in the EVEREST study. She wants to be among those receiving the stimulation implant, which she hopes will help regain the mobility to once again "pull my hair back in a ponytail," among other things.
"If I get the surgery, the reward will be some kind of a gain, some kind of improvement," she said. "That's what I'll be striving for, but you never know. Mother Nature is always in charge of things."
The studies are funded by the device's manufacturer, Seattle-based Northstar Neuroscience Inc.
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