Cause of Post-Polio Syndrome
The cause of post-polio syndrome is not known. However, research scientists believe that it is related to the remaining damage of individual nerve terminals after the initial poliovirus infection. Risk factors for post-polio syndrome include being female and having a permanent disability after recovery from the original poliovirus infection.
The cause of post-polio syndrome is not known. However, research scientists believe the characteristic new weakness of post-polio syndrome is related to the damage of individual nerve terminals in the motor units that remain after the initial poliovirus infection.
A motor unit is a nerve cell (or neuron) and the muscle fibers it activates. The poliovirus attacks specific neurons in the brain and spinal cord. In an effort to deal with the loss of these neurons, neurons that survive sprout new nerve terminals to the orphaned muscle fibers. The result is some recovery of movement and enlarged motor units.
Years of high use of these enlarged motor units adds stress to the neuron, which then may not be able to maintain the demands of all the new sprouts, resulting in the slow breakdown of motor units. Return of nerve function may occur in some fibers a second time, but eventually nerve terminals stop working and permanent weakness occurs. This explanation is consistent with the slow, stepwise, unpredictable course of post-polio syndrome.
While risk factors do not cause post-polio syndrome, certain factors can increase a person's risk for developing it. These risk factors include:
- Increasing length of time since acute poliovirus infection
- Presence of permanent disability after recovery from the original polio virus infection
- Being female.