What is post-polio syndrome?
Post-polio syndrome (PPS) is a condition that can strike polio survivors anywhere from 10 to 40 years after recovery from an initial attack of the poliomyelitis virus. PPS is characterized by a further weakening of muscles that were previously injured by polio infection. Symptoms include fatigue, slowly progressive muscle weakness, muscle and joint pain, and muscular atrophy. Some patients experience only minor symptoms, while others develop spinal muscular atrophy or what appears to be, but is not, a form of amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease. PPS is rarely life-threatening.
The extent to which polio survivors will suffer from PPS depends on how seriously they were affected by the first polio attack. Patients who had only minimal symptoms from the original attack and subsequently develop PPS will most likely experience only mild PPS symptoms. People originally hit hard by the polio virus may develop a more severe case of PPS with a greater loss of muscle function, difficulty in swallowing, and more periods of fatigue.
More than 300,000 polio survivors in the United States may be at risk for PPS. Doctors are unable to establish a firm incidence rate, but they estimate that the condition affects 25 percent to 50 percent of these survivors, or possibly more depending on how the disorder is defined.
PPS is caused by the death of individual nerve terminals in the motor units that remain after the initial attack of polio. This deterioration of individual nerve terminals might be an outcome of the recovery process from the acute polio attack. During this recovery process, in an effort to compensate for the loss of nerve cells (neurons), surviving motor neurons sprout new endings to restore function to muscles. This results in large motor units that may add stress to the body. As a result of this rejuvenation, the individual may have normal-functioning muscles for some time. But after a number of years, the motor neurons with excessive sprouting may not be able to maintain the metabolic demands of all their new sprouts, and a slow deterioration of the individual terminals may result.
Restoration of nerve function may occur in some fibers a second time, but eventually nerve terminals are destroyed and permanent weakness occurs. This hypothesis is consistent with PPS's slow, stepwise, unpredictable course. Through years of studies, scientists at the National Institute of Neurological Disorders and Stroke have shown that PPS is a very slowly progressing condition marked by long periods of stability.
Doctors arrive at a diagnosis of PPS after observing the patient and asking about symptoms. PPS may be difficult to diagnose in some because it is hard to determine what component of a neuromuscular deficit is old and what is new. Health professionals say that the only way to be sure a person has PPS is through a neurological examination aided by other laboratory studies that exclude all other possible diagnoses. Patients must visit the doctor periodically to establish that their muscle weakness is progressive.
Objective assessment of muscle strength in PPS patients may not be easy. A change in muscle strength is determined in specific muscle groups, or limbs, using various muscle scales, such as the Medical Research Council (MRC) scale or scales that quantify muscle force. Doctors use magnetic resonance imaging (MRI), neuroimaging, and electrophysiological studies, muscle biopsies analysis as tools to investigate the course of decline in muscle strength.
Once PPS is diagnosed, some patients worry that they have polio again, or even ALS. In general, PPS is not life-threatening. The only exception is in patients who experience severe respiratory impairment. Studies have proven that, compared to control populations, PPS patients lack any elevation of antibodies against the polio virus, and since PPS affects only certain muscle groups, it is not considered a recurrence of the original polio. Further, there is no evidence that the polio virus can cause a persistent infection in humans. Other studies have demonstrated that ALS, which progressively weakens muscles, does not occur more frequently in PPS patients, and PPS is not a form of ALS.
Scientists are working on a wide variety of treatment possibilities for patients with PPS, including drug treatments, some of which show promise. Doctors at the National Institutes of Health
(NIH) have tried treating PPS patients with alpha 2 recombinant interferon, but the treatment proved ineffective. A study in which PPS patients received high doses of prednisone demonstrated a mild improvement in their condition, but the results were not statistically significant. This, in addition to the drug's side effects, led researchers to recommend that prednisone not be used to treat PPS.
There has been much debate about whether to encourage or discourage exercise for polio survivors or individuals who already have PPS. Some doctors believe that too much exercise can worsen the patient's condition, and that rest will preserve energy. These doctors think patients will wear out their muscles by overusing them in exercise activities. However, others consider this notion unfounded and not scientifically documented.
There is much misinformation on this subject and many doctors do not know what effect exercise has on individuals with PPS. A commonsense approach, in which patients use individual tolerance as their limit, is currently recommended. Tolerance is the level at which one starts having discomfort or fatigue. Researchers at the NIH are addressing the exercise issue, not only to determine if exercise is helpful, harmful, or ineffective, but also to define the most effective type -- isotonic, isometric, isokinetic, or repetitive.
People who are polio survivors often ask if there is a way to prevent PPS. Presently, no prevention has been found. But doctors recommend that polio survivors follow standard healthy lifestyle practices: consuming a well-balanced diet, exercising in moderation, and visiting a doctor regularly.
Scientists are working on a variety of investigations that may someday help individuals with PPS. Some basic researchers are studying the behavior of motor neurons many years after a polio attack. Others are looking at the mechanism of fatigue, and trying to tease out information from the brain, muscles, and neuromuscular junction (the site where a nerve cell meets the muscle cell it helps activate). Trying to determine if there is an immunological link in PPS is also an area of intense interest. Researchers who discovered inflammation around motor neurons in the muscle are trying to find out if this is due to an immunological response.
Other investigators are searching for the polio virus, or mutated versions of it, fragments of which have been amplified from the spinal fluid. The significance of this finding is not known however, and more research is being done.
The National Institute of Neurological Disorders and Stroke conducts and supports a wide range of research on neurological disorders, including PPS. For information on the research programs of the NINDS, contact:
Office of Communications and Public Liaison
This information was prepared by
the Office of Scientific and Health Reports
July 1996 - NIH Publication No. 96-4030
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24580.010 Evaluation of Late Effects of Poliomyelitis