SCI Forum Reports
Recovery Research
March 7, 1997
"The spinal cord has the consistency of a noodle in chicken soup," said Steven A. Stiens, MD , a physiatrist at the Seattle Veterans Affairs Medical Center and an assistant professor in the UW Department of Rehabilitation Medicine. "When it gets bumped, it gets a contusion. The nerves are very fragile."
In incomplete injuries, the injury doesn't cross the entire spinal cord, and an area--usually around the outside of the cord--is spared. There are more sensory nerves than motor nerves in the central nervous system (CNS) or brain and spinal cord, so someone with an incomplete injury is more likely to have sensory function preserved than motor function. "That's probably better, because sensory function is protective," Stiens said. "It lets you know when you need to move."
In addition to the original injury, secondary damage to the nerves can occur as a result of inflammation. Immediately after an injury, the big effort in the emergency room is directed toward reducing this secondary damage. Vertebral alignment is important to get good blood flow along the surface of the spinal cord. Steroids limit inflammation and therefore make it more likely that the injury will be incomplete. Some people receive surgery to remove pressure from the spinal cord and protect those nerves that have been spared by the injury.
"In your car, you turn the key every time and it starts," Stiens said. "You'd be surprised if you turned the key and the trunk opened." Something similar happens in the spinal cord after an injury, however. During rehabilitation after SCI, spared nerves branch out to make new connections, a process that is improved by exercise.
Substances known as gangliosides, which are made up of sugar and lipid molecules, may be able to assist this process by providing lipid material for nerves to use while they are regenerating. Gangliosides are still a research drug, and have not been found to produce much functional improvement yet, Stiens said, but research is ongoing.
Asked how soon after injury such a drug would have to be used to be effective, Stiens said he doesn't know. "We're continually rebuilding our bodies. Cells are continually rebuilding themselves, neurons are continually reconnecting to themselves. That's how we learn, grow, and adapt."
Neurons grow about one millimeter per day. In the peripheral nervous system, cell processes will grow along a damaged nerve and reconnect. But in the CNS, damaged nerves only grow a short distance--2-3 millimeters--and then stop. "The central nervous system is a hostile area for nerve cell process growth," Stiens said. "The challenge of regeneration is to get the nerve message across the barrier of the injury."
One treatment possibility of the future would be to use peripheral nerve tissue as a bridge to connect the neurons above and below an injury in the hope that the nerves from the spinal cord would grow through the bridge. Another possibility involves transplantation of cells that aren't normally in the spinal cord to improve the environment for neuron growth, although animal experiments along these lines have met with little success. "If it doesn't work in a rat, it's probably not a good idea to experiment with treatment in humans," Stiens said.