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Nobody knows exactly what causes the signs and symptoms of post-polio syndrome to appear so many years after the first episode of polio. Currently, the most accepted theory regarding the cause of post-polio syndrome rests on the idea of degenerating nerve cells.

When poliovirus infects your body, it affects nerve cells called motor neurons — particularly those in your spinal cord — that carry messages (electrical impulses) between your brain and your muscles.

Each neuron consists of three basic components:

  • A cell body
  • A major branching fiber (axon)
  • Numerous smaller branching fibers (dendrites)

A polio infection often leaves many of these motor neurons destroyed or damaged. To compensate for the resulting neuron shortage, the remaining neurons sprout new fibers, and the surviving motor units become enlarged. This promotes recovery of the use of your muscles, but it also places added stress on the nerve cell body to nourish the additional fibers. Over the years, this stress may be more than the neuron can handle, leading to the gradual deterioration of the sprouted fibers and, eventually, of the neuron itself.

Another theory is that the initial illness may have created an autoimmune reaction, causing the body's immune system to attack normal cells as if they were foreign substances.

Mar. 03, 2011