Post-polio syndrome (PPS) is a condition that affects
polio survivors anywhere from 10 to 40 years after recovery from an
initial paralytic attack of the poliomyelitis virus. PPS is characterized
by a further weakening of muscles that were previously affected by the
polio infection. Symptoms include fatigue, slowly progressive muscle
weakness and, at times, muscular atrophy. Joint pain and increasing
skeletal deformities such as scoliosis are common. Some patients
experience only minor symptoms, while others develop spinal muscular
atrophy, and very rarely, 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 original 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, who were left with severe residual
weakness, 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 neuronal cell
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 by observing the patient and
asking about symptoms, and by excluding other disorders. 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, or spinal fluid analysis as tools to investigate
the course of decline in muscle strength and exclude other conditions.
Once PPS is diagnosed, some patients worry that they have polio again,
or even ALS. In fact, they have neither of these disorders. In general,
PPS is not life-threatening. The only exception is in patients left with
severe residual respiratory difficulties, who may experience new 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.
In an effort to reduce fatigue in PPS patients, scientists conducted a
study using low doses of the drug pyridostigmine (Mestinon). A large,
controlled study that has been recently completed showed that
pyridostigmine is not helpful for PPS patients. In a controlled study
conducted by NIH scientists, the drug amantadine also was not helpful in
reducing fatigue.
The future in PPS treatment may center around nerve growth factors. One
small study that NINDS scientists participated in showed that insulin-like
growth factor (IGF-1), which can enhance the ability of motor neurons to
sprout new branches and maintain existing branches, was not helpful. Since
PPS results from the degeneration of nerve sprouts, other growth factors
may target the heart of the problem and help to regenerate new nerve
sprouts.
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.
Researchers at the NIH recently conducted a study of exercise in PPS,
not only to determine if exercise is helpful, harmful, or ineffective, but
also to define the most effective type -- isotonic, isometric, isokinetic,
or repetitive. Their study showed that exercise is safe and effective, and
other investigators have had similar findings. 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.
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.
Keeping on Top of Your Condition
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BRAIN
P.O. Box 5801
Bethesda, MD 20824
(800) 352-9424
http://www.ninds.nih.gov/
International Polio Network/Gazette International
4207 Lindell
Boulevard, #110
St. Louis, Missouri 63108-2915
(314) 534-0475
http://www.post-polio.org/
Polio Connection of America
P.O. Box 182
Howard Beach, NY
11414
(718) 835-5536
http://www.geocities.com/w1066w/
March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
resourcecenter@modimes.org
914-428-7100
888-MODIMES
(663-4637)
http://www.modimes.org/
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