Common signs and symptoms of post-polio syndrome include:

• Progressive muscle and joint weakness and pain
• General fatigue and exhaustion with minimal activity
• Muscle atrophy
• Breathing or swallowing problems
• Sleep-related breathing disorders, such as sleep apnea
• Decreased tolerance of cold temperatures

In most people, post-polio syndrome tends to progress slowly, with new signs and symptoms followed by periods of stability.

There are several theories as to what causes post-polio syndrome, but no one knows for sure.

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 damages or destroys many of these motor neurons. To compensate for the resulting neuron shortage, the remaining neurons sprout new fibers, and the surviving motor units enlarge.

This promotes recovery of the use of your muscles, but it also pushes 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.

Factors that can increase your risk of developing post-polio syndrome include:

• Severity of initial polio infection. The more severe the initial infection, the more likely that you'll have signs and symptoms of post-polio syndrome.
• Age at onset of initial illness. If you developed polio as an adolescent or adult rather than as a child, your chances of developing post-polio syndrome increase.
• Recovery. The greater your recovery after acute polio, the more likely it seems that post-polio syndrome will develop, perhaps because greater recovery places additional stress on motor neurons.
• Excessive physical activity. If you often exercise to the point of exhaustion or fatigue, you might overwork already stressed-out motor neurons and increase your risk of post-polio syndrome.

Post-polio syndrome is rarely life-threatening, but severe muscle weakness can lead to complications:

• Falls. Weakness in your leg muscles makes it easier for you to lose your balance and fall. You then might break a bone, such as a hip, leading to other complications.
• Malnutrition, dehydration and pneumonia. People who've had bulbar polio, which affects nerves leading to muscles involved in chewing and swallowing, often have difficulty with these activities as well as other signs of post-polio syndrome.

Chewing and swallowing problems can lead to inadequate nutrition and to dehydration, as well as to aspiration pneumonia, which is caused by inhaling food particles into your lungs (aspirating).

• Chronic respiratory failure. Weakness in your diaphragm and chest muscles makes it harder to take deep breaths and cough, which can cause fluid and mucus to build up in your lungs.

Obesity, smoking, curvature of the spine, anesthesia, prolonged immobility and certain medications can further decrease your breathing ability, possibly leading to a sharp drop in blood oxygen levels (acute respiratory failure). You might then need treatment to help you breathe (ventilation therapy).

• Osteoporosis. Prolonged inactivity and immobility are often accompanied by loss of bone density and osteoporosis in both men and women. If you have post-polio syndrome, talk to your doctor about bone-density screening.