Post-polio syndrome is a slowly progressing weakness that affects polio survivors decades after their initial bout with the disease.
Description
In order to understand post-polio syndrome, it's important to understand polio infection in general. Although people of any age can become infected with poliovirus, it tends to infect young children in particular. About 1% of all people who become infected with poliovirus will actually become ill. Initial symptoms include fever, nausea,
and vomiting, followed by several symptom-free days. Some individuals then recover completely. Others go on to develop new symptoms, including severe head, back, and neck pain. These symptoms signal that the virus is invading the nervous system, causing inflammation, injury, and destruction of motor nerves (the nerves that are necessary for muscle movement). As motor nerves are destroyed, the muscles cannot receive messages from the brain. Without input from the brain, muscle tone becomes weak and floppy, and paralysis sets in. Over time, the muscle becomes atrophic (shrunken in size). Paralysis is usually asymmetric; that is, it affects only one side of the body. The paralyzed limbs retain their ability to feel. When the muscles of respiration are affected, the patient may need to be put on a mechanical ventilator.
It only takes a few days for the weakness and/or paralysis to progress to its maximum level of severity. Recovery continues for about six months, during which time the remaining unaffected motor nerves begin sprouting new branches to the muscles, in an attempt to compensate for the nerves that were completely destroyed. During this phase, the patient will regain some degree of functioning. After six months have passed, whatever disability remains will usually be permanent.
Post-polio syndrome occurs some decades after the original infection with polio. Initially, the subtly gradual progressive muscle weakness is barely noticed by the patient, but over time the decrement becomes increasingly obvious. In general, the more severe the original polio infection, the more severe the disability from post-polio syndrome.
Demographics
Only 1% of all people infected with poliovirus actually develop full-fledged polio. About 25-50% of polio survivors will eventually be affected with post-polio syndrome.
Causes and symptoms
Attempts to completely delineate the process by which post-polio syndrome develops have not been totally successful. A number of working theories have been developed.
The newer nerve sprouts that grew in order to compensate for lost motor units overtax the rest of the nerve, and over time the nerve begins to fail.
Injured nerves that regained function end up failing after years of overuse attempting to compensate for lost motor units.
Remaining particles of the poliovirus may precipitate a chemical response in the immune system that accidentally destroys the body's own nerves.
Spinal cord changes in polio survivors may adversely affect nerves over time.
Symptoms of post-polio syndrome include severe fatigue; decreased energy; gradually progressive muscle weakness and muscle atrophy; involuntary muscle twitching (fasciculation); muscle, joint and back pain; difficulty breathing and swallowing; and problems with sleep. The most severe muscle problems seem to occur in those muscles that were already affected by the initial bout of polio, although muscles that were not originally affected may also develop some new degree of weakness.
Diagnosis
Diagnosis should be suspected in any polio survivor experiencing new muscle weakness.
Four criteria are required to diagnose post-polio syndrome in a patient with gradually increasing muscle weakness:
known history of poliovirus infection with residual muscle weakness
history of recovery of some degree of muscle function, with a period of stability lasting at least 15 years
at least one limb demonstrating residual muscle atrophy, weakness, lack of normal reflex, and continued normal sensation
normal function of sphincter muscles (the muscles around the anus and the lower part of the esophagus)
Treatment team
The treatment team will depend in part on the specific symptoms encountered. In general, once diagnosed, the patient will benefit from work with a physical therapist, occupational therapist, and speech and language therapist. Specialists in arthritis, orthopedics, rehabilitation, and pulmonology may also be helpful.
Treatment
There is no cure for post-polio syndrome. Efforts are primarily directed at retaining mobility and improving patient comfort. Anti-inflammatory medications can help relieve muscle and joint pain by decreasing inflammation. Braces, wheelchairs, or motorized scooters may help very compromised patients retain some independence and mobility. Respiratory and sleep problems may interact with each other to create considerable distress. They may be relieved by the use of supplemental oxygen and/or breathing devices to help keep the airway open while sleeping.
Recovery and rehabilitation
The physical therapist should design a thoughtful exercise program to maintain and increase flexibility, although it is important not to overtax already weakened muscles and nerves. Occupational therapy can help the individual learn methods to compensate for muscle weakness, and still retain independence in the activities of daily living. Speech and language therapists can be helpful for swallowing problems.
Clinical trials
A clinical trial through the National Institute of Neurological Disorders and Stroke is studying whether the drug modafinil might be helpful in treating the relentless fatigue of post-polio syndrome.
Prognosis
Because the increase in muscle weakness is so gradual, post-polio syndrome is generally thought to have a good prognosis, rarely causing significantly more severe impairment and disability. In a few rare cases, however, progressive weakening of the muscles of respiration can result in death.
BOOKS
Modlin, John F. "Poliovirus." In Principles and Practice of Infectious Diseases, edited by Gerald L. Mandell. London: Churchill Livingstone, Inc., 2000.
Nath, Avindra, and Joseph R. Berger. "Poliomyelitis." In Cecil Textbook of Medicine, edited by Lee Goldman. Philadelphia: W.B. Saunders Company, 2003.
Roos, Karen L. "Viral Infections." In Textbook of Clinical Neurology, edited by Christopher G. Goetz. Philadelphia: W.B. Saunders Company, 2003.
WEBSITES
National Institute of Neurological Disorders and Stroke (NINDS). Post-polio Syndrome Fact Sheet. Bethesda, MD: NINDS, 2003.
