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For years polio was one of the most feared diseases in America, responsible for crippling, paralysis and death. In 1952, according to the Centers for Disease Control and Prevention, it reached its peak in the United States with more than 21,000 paralytic cases. Shortly after, vaccines were developed that greatly reduced its spread. Today, few people in developed countries get polio, and the disease is well on its way to being eliminated in developing countries, thanks to immunization efforts with polio vaccine.

But for some people, the initial problems they had with polio are reappearing as a condition called post-polio syndrome (PPS). The cause is unknown, but research is beginning to yield a better understanding of this complex syndrome.

According to the National Institute of Neurological Disorders and Stroke (NINDS), the condition affects about one in four polio survivors, perhaps even more depending on how the disorder is defined.

Treatment is aimed at managing the signs and symptoms associated with PPS and increasing quality of life.

Post-polio syndrome refers to a cluster of disabling signs and symptoms that appear decades — between 10 and 40 years — after the initial illness. Common signs and symptoms include:

• New muscle weakness in limbs that were originally affected or in limbs that didn't seem to have been affected at the time
• General fatigue and exhaustion with minimal activity
• Muscle and joint pain
• Breathing or swallowing problems
• Sleep-related breathing disorders, such as sleep apnea
• Decreased tolerance of cold temperatures

Nobody knows exactly what causes these signs and symptoms to appear so many years after the first episode of polio. Currently, the most accepted theory regarding the cause of PPS 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)

Nerve cells communicate with adjacent nerve cells at contact points called synapses. Electrical impulses run along extended chains of these neurons until they reach their desired destination, as when your brain sends a message to the muscles of your legs and feet to step forward.

A polio infection often leaves many of these motor neurons dead 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 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, the neuron itself.

Normally, everyone loses some neurons through the aging process. But people who've had polio may have lost so many to begin with that they end up with fewer neurons than people who've never had polio. This may lead to the progressive weakness characteristic of PPS. Currently, little evidence suggests that people with polio lose neurons at a faster rate than normal.

Some scientists theorize 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. But the evidence surrounding this theory is limited, compared with the studies supporting the more generally accepted motor neuron degeneration theory.

It's possible that some of the signs and symptoms of PPS, especially joint pain, may be due to chronic overuse of muscles that apparently were undamaged by the initial phase of polio. For example, if your left leg was disabled by polio, it may be that your right leg develops complications later in life because its muscles and joints have had to overcompensate for the disabled leg.

Factors that may increase your risk of developing PPS include:

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

If you're experiencing weakness or fatigue that seems to be slowly getting worse, see your doctor. It's important to rule out other causes of your signs and symptoms that may require different therapy from what's currently advised for PPS.

To arrive at a diagnosis of PPS, doctors look for three indicators:

• Previous diagnosis of polio. This may require finding old medical records or getting information from older family members, because acute polio primarily occurs during childhood. The late effects of polio usually occur in people who were age 10 or older during the initial attack of polio and whose symptoms were often severe.
• Long interval after recovery. People who recover from the initial attack of polio often live for many years without further symptoms. The onset of late effects varies widely but typically begins 10 to 40 years after the initial diagnosis.
• Gradual onset. Weakness tends to be imperceptible until it interferes with daily activities. You may awaken refreshed but feel exhausted by the early afternoon, tiring after activities that were once easy.

In addition, because the signs and symptoms of post-polio syndrome are similar to those commonly associated with other disorders, your doctor will attempt to exclude other possible causes, such as arthritis, fibromyalgia, chronic fatigue syndrome or scoliosis.

Some people with post-polio syndrome worry that they may be getting amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease. But the late effects of polio are not a form of ALS.

Some of the tests your doctor may use to rule out alternative diagnoses include:

• Electromyography (EMG) and nerve conduction studies. Electromyography measures the tiny electrical discharges produced in muscles. A thin-needle electrode is inserted into the muscles your doctor wants to study. An instrument records the electrical activity in your muscle at rest and as you contract the muscle. In a variation of EMG called nerve conduction studies (NCS), two electrodes are taped to your skin above a nerve to be studied. A small shock is passed through the nerve to measure the speed of nerve signals. These tests help identify and exclude conditions such as neuropathy, an abnormal condition of your nerves, and myopathy, a muscle tissue disorder.
• Imaging. You may undergo tests such as magnetic resonance imaging (MRI) or computerized tomography (CT) to produce images of your brain and spinal cord. These tests can help exclude spinal disorders such as spondylosis, a degenerative spine condition, or spinal stenosis, a narrowing of your spinal column that puts pressure on your nerves.
• Blood tests. People with PPS usually have normal blood samples. Abnormal blood test results may indicate another underlying problem that's causing your symptoms.

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. A fall may result in a broken bone, such as a hip fracture, leading to other complications.
• Malnutrition, dehydration, 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 symptoms of PPS. Chewing and swallowing problems can lead to inadequate nutrition and dehydration, as well as aspiration pneumonia, which is caused by inhaling (aspirating) food particles into your lungs.
• Acute respiratory failure. Weakness in your diaphragm and chest muscles makes it harder to take deep breaths and cough, which ultimately leads to accumulation of fluid and mucus in your lungs. Obesity, curvature of the spine, anesthesia, prolonged immobility and certain medications can further decrease breathing ability, possibly leading to acute respiratory failure. This is characterized by a sharp drop in blood-oxygen levels and may require you to undergo ventilation therapy (positive pressure ventilation). If you're to have surgery, even dental surgery, and require general anesthesia, let your doctor or dentist know that you have PPS. Even people with PPS who seem healthy may have respiratory difficulties.
• Osteoporosis. Prolonged immobility and paralysis is often associated with loss of bone density and osteoporosis, in men as well as women. If you have PPS, you may wish to be screened for osteoporosis.

Because the signs and symptoms often vary, there's no one specific treatment for PPS. The goal of treatment is to manage your symptoms and help make you as comfortable and independent as possible.

• Energy conservation. This is probably the most important aspect of managing PPS. It involves pacing your physical activity and combining it with frequent rest periods to reduce fatigue. Assistive devices, such as a cane, walker, wheelchair or motor scooter, also can help you conserve energy.
• Physical therapy. Your doctor or therapist may prescribe exercises for you that strengthen your muscles without inducing muscle fatigue. These usually include less strenuous activities, such as swimming or water aerobics, that you perform every other day at a relaxed pace. Exercise to maintain fitness is important, but be cautious in your exercise routine and daily activities. Avoid overusing your muscles and joints and attempting to exercise beyond the point of pain or fatigue. Otherwise, you may need several days' rest to regain your strength. A therapist can even show you ways to breathe that help conserve energy.
• Occupational therapy. A physical or occupational therapist can help you modify your home environment so that it's safe and convenient for you. This may include installation of grab bars in the shower or a raised toilet seat. Your therapist may also help you rearrange furniture or rethink certain household or work-related tasks, decreasing the number of steps you must take and increasing your efficiency.
• Speech therapy. A speech therapist can show you ways to compensate for swallowing difficulties.
• Sleep apnea treatment. Treatment for sleep apnea, which is common among people with PPS, may involve changing your sleeping patterns, such as avoiding sleeping on your back, or using a device that helps open up a blocked airway.
• Medications. Medications, including aspirin and other nonsteroidal anti-inflammatory drugs, may ease muscle and joint pain. Certain drugs — pyridostigmine (Mestinon), amantadine (Symmetrel), selegiline (Eldepryl) and bromocriptine (Parlodel) — have been studied as a treatment for PPS fatigue, but no clear benefit has been shown. Other medications for fatigue may help, such as modafinil (Provigil). Studies of insulin-like growth factor-1 (IGF-1), a medication designed to improve muscle strength, showed that although it didn't change strength or susceptibility to fatigue, it did improve recovery after exercise.

Having to deal again with an illness you thought you had dealt with can be discouraging, even overwhelming at times. Recovering from the initial illness required drive and determination on your part, but now the late effects of polio require you to rest and conserve your energy. Moving from one frame of mind to another can be a difficult switch. Here are some suggestions that may help:

• Limit activities that cause pain or fatigue. Moderation is key. Overdoing it on a good day can lead to several subsequent bad days.
• Be smart. Conserving your energy through lifestyle modifications and assistive devices doesn't mean you're giving in to the illness. It just means you've found a smarter way to deal with it.
• Stay warm. Cold increases muscle fatigue. Keep your home at a comfortable temperature and dress in layers, especially when you go out.
• Avoid falls. Get rid of throw rugs and loose clutter on the floor, wear good shoes, and avoid slippery or icy surfaces.
• Maintain a healthy lifestyle. Eat a balanced diet, stop smoking and decrease caffeine intake to keep fit, breathe easier and sleep better.
• Get support. It's not a crime to lean on your friends and family for support. In most cases, they're looking for ways to help you, and you can help them by telling them how. You may even consider joining a support group for people with PPS. Sometimes, just talking things over with people who have similar problems enables you to better cope with the challenges at hand.