Polio - Causes of post-polio syndrome

The exact cause of post-polio syndrome (PPS) is unknown. 

The main theory is that it may be caused by the gradual deterioration of nerve cells in the spinal cord (motor neurones), which were damaged by the polio virus during a previous infection.

Motor neurone cells are used by your brain to send signals to your muscles. These cells are targeted by the polio virus.

A polio infection can damage motor neurone cells, leading to a shortage of motor neurones. To compensate for this shortage, the body will enlarge the remaining motor neurones, leading to a recovery of movement in the affected limbs.

It is thought that excessive prolonged use of these enlarged motor neurones may weaken them and the cells may start to break down over the course of many years. This is thought to lead to the muscle weakness, muscle wasting and fatigue associated with PPS.

This theory would also explain why PPS can take years to appear, and why it often has slow and progressive symptoms with periods where normal activity is possible.

Although PPS can only develop in people who have been infected with polio in the past, PPS itself is not contagious. A theory that the polio virus may lie dormant in your body after the original infection, causing PPS when it becomes reactivated at a later stage, has been disproven.