Intensive exercise offers hope to those with spinal injuries
Most people with serious spinal cord injuries have faced poor odds and a short window of opportunity for regaining lost mobility.
They’re unlikely to recover function below the point where the spinal cord has been damaged, doctors and rehabilitation specialists have said, and any chance of regaining mobility and sensation lasts for about only a year. Some researchers, however, maintain that such patients have a much greater chance of recovery than has long been believed. Led by V. Reggie Edgerton, an exercise physiologist at UCLA’s Brain Research Institute, they’re attempting to prove that the spinal cord can control motor function, even if the connection to the brain is severely damaged, and that long-term paralysis isn’t always irreversible.
This radical notion became widely publicized last year, when actor Christopher Reeve announced that he had regained some movement and sensation after starting a physical therapy regimen inspired by such research.
Experiments conducted over the last two decades by Edgerton, along with a handful of other researchers, suggest that intensive exercise can reactivate the ability to move below where the spinal cord is harmed.
“Edgerton busted the field wide open,” says Hans S. Keirstead, a neuroscientist with the Reeve-Irvine Research Center at the UC Irvine College of Medicine. “He proved the spinal cord could be retrained through aggressive exercise.”
Most scientists have long believed that the signals controlling movement come directly from the brain, and that the spinal cord is merely a conduit for these nerve impulses. Once that connection is disturbed, they say, those messages can’t be relayed to the nerves that regulate locomotion. As a consequence, traditional rehabilitation has focused on reducing pain and strengthening muscles above the injury to help compensate for lost mobility.
In contrast, Edgerton theorized that the spine is a “central pattern generator,” a minicomputer that can drive motor activity, such as walking, independently of the brain. He also believes the spine has an internal memory program, which could be reawakened by a program of patterned exercise.
He began his work in the early ‘80s, experimenting on cats whose spinal cords had been cut midway down their back, which paralyzed their hind legs. The animals were placed in a suspended harness and put on a modified treadmill. Their limbs were moved in a stepping motion to see if constant repetition of a walking motion could reactivate the motor neurons in the spinal cord. After three to six months, most of the cats could walk again. Although the regimen didn’t regenerate damaged nerves, says Edgerton, it seemed to kick-start “the functional capacity of the neural circuitry below the lesions.”
German scientists later tested Edgerton’s program on humans. Some of the volunteers had been injured a few weeks before starting therapy; others had sustained injury years earlier. Their spinal cords had been damaged, not severed, however; though their movements were sharply limited, they weren’t paralyzed.
After completing the regimen, of the 33 patients who had been relying on wheelchairs, 25 were able to walk independently, seven could walk with assistance and one showed no improvement. Only one member of the control group, which received traditional therapy, could walk without help. When the study results were published in 1995, it changed the way rehabilitation was done in Germany.
“It is now considered unethical not to have this treatment for spinal cord injury patients,” Edgerton says.
In the last decade, about three dozen patients with damaged spinal cords have undergone an experimental 12-week training program in the UCLA Brain Research Institute laboratory, where they are put in a suspended harness and therapists move their limbs on a treadmill in a pattern that mimics walking. The training schedule varies, depending on the severity of the injury and patients’ endurance (their muscles often are atrophied from disuse, so they don’t have much stamina). Typically, the program entails three to five workouts a week, and patients build to three 10-minute sessions on the treadmill.
Their recovery has varied, but some have regained as much as 30% of motor function. These results have prompted a larger, ongoing clinical trial of about 100 patients with partially cut spinal cords at six sites in the U.S. and Canada.
“There’s now a lot of evidence that the human spinal cord can learn and remember,” says Susan J. Harkema, a physiologist who helps conduct the UCLA research. “Now we’re trying to figure out the best way to take advantage of that knowledge.”
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Therapy could reduce harm to spinal tissue
Spinal cord injury is a two-stage process. The injury itself causes the initial trauma, but the immune system can do even more damage.
Because the body’s natural response induces swelling, soft tissue is pressed against the rigid spinal column, which can harm nerves and the spinal cord. Immune cells, known as T-cells, also can create toxic compounds that attack spinal tissue and nerves.
A new drug developed by UC Irvine researchers may halt this process, sparing tissue that otherwise would have been lost. The therapy is composed of an antibody (a protein produced by the immune system) that is programmed to latch onto the harmful immune system cells, stopping the destructive reaction.
In a 2003 test on 19 rats with spinal cord injuries, the 11 animals in the treated group had 70% less spinal damage than the group of eight untreated rats. “The difference in mobility between the treated and untreated rats was dramatic,” says Hans Keirstead, a UC Irvine neuroscientist who helped develop the drug. Human trials are expected to start soon.
