Question: About 20 years ago at one of your conferences, the state of the art said “neurogenesis in muscles affected by polio was limited. The nerves died, new sprouts formed new nerves, but these new sprouts only had a 50-year life span, and thus, post-polio. Therefore, don’t overuse your affected muscles.” I need new motor neurons in my left calf. I’m studying neuroscience this semester and read that adult neurogenesis occurs in the dentate gyrus, sub-ventricular zone, striatum and cerebellum. The striatum has motor function. Is there new data? Is it still true that overuse will kill those original sprouts and therefore the new nerves? Is exercise now recommended, or is stem cell injection the only way to form new motor neurons in degraded muscle?
Dr. Maynard: Thank you for your thoughtful questions concerning neurogenesis after paralytic polio. The leading theory for post-polio syndrome remains distal degeneration of enlarged motor units many years later after the initial polio infection with nerve damage. There is little new data to explain what triggers the late degeneration. Compared to 20 years ago, most clinicians who see many polio survivors recognize that “exercise” remains important for preventing further weakening and that too much exercise (as manifest by transient overuse weakness) is likely to hasten weakening from further denervation of enlarged motor units. I recommend careful individual evaluation to consider possible exercise prescriptions to meet realistic goals and to be compatible with one’s past and current (examination based) capabilities and functional demands (intensity and duration of daily activities). Stem cell injections have shown some promise for neurogenesis in the central nervous system but NOT in motor nerve cells of the spinal cord whose long axons reach voluntary muscle and are the basis of the peripheral nervous system.
Post-Polio Health (Vol. 37, No. 4, Winter 2021)