SCI Forum Reports

Recovery Research Update

March 5, 1996

Steven A. Stiens, MD , is an assistant professor in the UW Department of Rehabilitation Medicine and a physiatrist at the Seattle Veterans Affairs Medical Center. He also has T2-level paraplegia, "so I have an ongoing personal interest in regeneration and recovery...and my patients are always interested in it," Stiens said.

Nerves are communication pathways in the body. They are made up of bundles of neurons, which are specialized cells with long branches called processes. When stimulated, a neuron carries an electric signal along its body and releases chemicals called neurotransmitters from the ends of its "sending" processes, which are called axons. These chemicals carry the signal to the next neuron, which passes the signal on in the same way.

"Neurons are happy and healthy if they're connected to other nerve cells," Stiens said. "If they're not, they shrink." Under normal conditions, a neuron carries a signal in only one direction -- either away from the brain, to produce movement, or toward the brain, to deliver sensory information. A nerve can be made up of both motor and sensory neurons. One example is the median nerve, which brings both sensation and movement to part of the hand.

"Most animals have more sensory than motor nerves," Stiens said, "so if you damage the nervous system and there's anything left, it's likely to be sensory." This is just as well, since preserved sensation without movement is more useful and protective than preserved movement without sensation, he said.

There are two types of motor nerves. One brings movement messages into the spinal cord from the brain (these are called Upper Motor Neurons or UMNs), and the other brings movement messages out of the spinal cord and into the muscles (these are called Lower Motor Neurons or LMNs). A high spinal cord injury can damage the UMNs and leave the LMNs intact. Without signals from the brain, the LMNs can fire on their own, causing spasms in the muscles. People with paraplegia can have UMN or LMN lesions, Stiens said, while those with tetraplegia usually have UMN lesions, and usually have a lot of spasms of the legs.

The spinal cord is fragile, floating in salty liquid like a soft noodle in chicken-noodle soup. It is made up of gray matter at the center, where the neuron cell bodies are, and white matter, which is a collection of axons running together. In most cases, SCI does not sever the spinal cord, but only bruises it. A bruise and the resulting inflammation are enough to interrupt the relay of signals across neurons. Once this occurs, recovery is inhibited by the white matter of the spinal cord itself, which is a hostile environment for nerve process growth -- probably in an effort to keep the complex "wires" of the nervous system from crossing.

Still, people do recover to some extent after SCI, even without drugs or medicine, Stiens said. "I tell patients that they're going to get meaningful recovery for at least a year." This recovery is probably due to growth and branching by spared nerves, which then form new connections and restore some lost function or sensation.

At present, acute treatment for SCI is aimed at preventing further injury and enhancing this natural recovery process as much as possible. Making sure the vertebrae are properly aligned, eliminating pressure on the spinal cord from bone fragments, and using steroids to reduce inflammation are all designed to protect the cord from sustaining additional damage.

Exercise helps enhance and maintain natural recovery, so "whatever function you do have, you should use it," Stiens said. "If you continue to do things, provide the demands, your body will continue to meet those demands...so it's kind of a 'use it or lose it' situation."

A number of research projects are looking into possible ways to produce a permissive environment to help nerves grow. One area of study involves gangliosides, substances that are normally present in cell membranes and assist in the process of cell repair. When given intravenously for a couple of months after injury, gangliosides seem to provide some improvement in motor recovery, though this improvement has not yet been shown to be functionally meaningful, Stiens said.

Other studies are using nerve tissue from the peripheral nervous system, where growth is not inhibited, to make a "bridge" between the neurons above and below a spinal cord injury. So far, these studies have succeeded in making nerve processes grow into the bridge tissue, but "once they made it (back) into the spinal cord white matter, they stopped growing and did not reconnect," Stiens said.

Very recent studies have shown some growth of nerve processes through multiple peripheral nerve bridges into the gray matter in rats, and have noted some limited recovery of movement.

Another direction of current research is transplantation of tissue from fetal spinal cords, where growth and branching of nerves is not inhibited, into the injured part of the spinal cord. Animal studies have produced some positive results, and some clinical studies of fetal transplants have been done in humans with Parkinson's Disease, but more animal studies are needed to evaluate the safety and effectiveness of this procedure and determine essential details, such as the most appropriate cell types to transplant and the optimal time after injury for transplantation, before it can be tried in humans with SCI.

Other studies are looking into growth factors, or chemicals that promote nerve growth, and electrical stimulation, Stiens said. If such techniques ever succeed in permitting nerves to grow and reconnect in the spinal cord, "you may not get the right connection, but that's OK," because the brain may learn to use the new pathways, as it does with muscle transfers.

As new ideas come along, people with SCI may be faced with the bewildering question of whether they should undergo a new treatment or participate in a clinical study. "To be a good consumer, you should think scientifically," Stiens said, offering six questions that participants should consider concerning new or experimental treatments:

Have there been prior animal studies with results indicating that the treatment will be effective in humans?
Have there been prior human studies demonstrating success?
Has the study or treatment been approved by a human subject committee?
Are the costs of the study covered by a grant?
Are the costs of the treatment covered by insurance?
Is the hospital where the treatment will take place accredited?

"The best experiments are approved experiments, and the best participants are informed participants," he said.