The Late Effects of Polio: Do you know the signs?

By Polio Australia

Pathophysiology of the Late Effects of Polio (LEoP) Acute poliomyelitis (polio, also known as 'infantile paralysis') is a viral infection affecting the nervous system. It can infect both the central and the peripheral nervous system, but the most common infection is in the anterior motor horn cells, resulting in flaccid paresis of the muscles. This can present as a widely variable distribution of weakness in skeletal and bulbar musculature, with residual impairment and paralysis ranging from minor muscle weakness to total paralysis requiring intervention such as ventilation.

After motor-neuron destruction during the acute polio phase, surviving motor units sprout axons to reinnervate the denervated or ‘orphaned’ muscle fibres. This process of denervation and reinnervation is ongoing over the muscle lifespan. As a consequence, polio-affected muscles have oversized motor units and increased muscle-fibre density. It is thought that these large motor units result in increased weakness as they ‘drop out’ due to ageing and/or overuse. Due to this process, people with LEoP may have experienced a prolonged period of stability of physical symptoms such as weakness and pain, often lasting several decades, before presenting to their primary care provider with what can feel like a resurgence of polio-like symptoms.

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