Scientists report in the Lancet a case of a 23 year old man paralyzed from the chest down who was able to learn to stand and walk with the aid of a spinal stimulator. This is an interesting advance, but news reports are careful to point out (correctly) that it is not a cure.
Rob Summers suffered an car accident in 2006 that damaged his spinal cord at the T1 level – just below the neck. This would mostly (although not completely) spare his arms, but render him weak in the legs. According to the case report he had no detectable leg movement and lost bladder control but had partial sensation in the legs. This is an important detail to put this case into perspective – Summers’ injury was partial, if severe. This means there were some neurons that were spared.
When I first read the news items but had not yet read the original report I thought this might be another case of using electrical stimulation for external control. There are already systems in existence, called functional electrical stimulation (FES), that allow paraplegics to externally stimulate their leg muscles, to make them contract in a sequence that causes them to take clumsy if functional steps. Simple devices strap onto the lower leg and can treat foot drop by stimulating the muscle that raises the foot at t the ankle. More elaborate devices consist of a walker with hand controls that stimulate various muscles of the legs and allow for a clumsy but functional gait.
FES devices are useful in selected cases. They take a great deal of training, and work best in those who are in good shape at baseline. They also require a lot of effort. But anything that provides any function is welcome to those paralyzed by spinal cord injury or other neurological injury.
This case does not involve FES. Rather, 16 electrodes were placed on the dura, the lining on the outside of the spinal cord, at the lumbosacral levels in the lower back. While the stimulator was running Summers then trained, first to stand and then later to walk. He was able to regain some voluntary control of his muscles, and even regained some bladder function – although only when the stimulator was running. The researchers speculate that he must have had some surviving neurons that were not functional, but are coaxed into function by the electrical stimulation. In addition, after extensive training, plasticity may have restored some connections. And further, sensory feedback from the relatively spared sensory pathways may also be contributing to motor activation.
This is a nice advance, and will likely provide some functionality to selected patient with paraplegia. But this approach has limits. The most obvious is that it will likely only work in patients who have some preserved spinal cord – a complete lesion will not be amenable to this intervention.
I further wonder what the effect of this treatment is on spasticity and atrophy. The loss of connections to the the motor neurons below the injury removes their tonic inhibition, causing them to be hyperactive. This results in spasticity – uncontrolled contractions of the muscles. This is a big problem in paralyzed patients, especially from spinal cord injury.
Another problem is atrophy of the weakened muscles. Lack of activation through the normal pathways causes the muscles to shrink. Stimulating the muscles or nerves to those muscles does not reverse or even avoid this atrophy. The question is – with this new treatment activate the muscles in a way that will reverse some of the muscle atrophy?
It should also be noted that Summers is a young patient who was athletic before his injury. So he is an ideal candidate for this system. This is similar to FES, where companies showcase their star clients. But it must be emphasized that such results may not be typical for the average patient.
Despite my caveats, this is a nice advance. Like most medical advances these days, it is an encouraging step in the right direction. It should not be thought of as a cure or even as a potential treatment for every patient. Each such advance, however, is cumulative and gives us more options.
This represents one type of approach to spinal cord (and perhaps even brain) injury. We can take a cellular approach – treating the cells themselves, trying to get them to regenerate, or replacing them with stem cells. Or we can “hack” the nervous system, exploiting the fact that it is an electrical organ system. These are complementary approaches, and it will be interesting to see which approach has more potential in the future. Will people with paraplegia in the near future primarily be treated by having stem cells and hormones injected into their spinal cords, or by having computers and electrodes implanted?
Both approaches show promise.