For release: Sunday, April 21, 1991
Many post-polio patients have swallowing abnormalities that increase the risk of choking but are unaware of their condition, according to a study directed by a scientist at the National Institute of Neurological Disorders and Stroke (NINDS) and published in the April 25 issue of the New England Journal of Medicine .* .
Of the 500,000 Americans who survived acute polio, more than 125,000 now have post-polio syndrome, in which progressive muscle weakness develops 25 to 30 years after the initial disease.
Previous reports have demonstrated that post-polio syndrome weakens the muscles of the arms and legs — causing patients difficulty when walking, lifting, or reaching. The recent study shows that this progressive weakness also affects the bulbar muscles of the tongue, mouth and throat and triggers swallowing problems — called dysphagia — in most patients.
"These findings should prompt physicians to check their post-polio patients closely for abnormal swallowing," said Marinos C. Dalakas, M.D., the NINDS scientist who directed the study. "Unlike new weakness in the arm or legs, which causes obvious problems with movement, deterioration in swallowing is easily overlooked — even with standard neurological exams," Dr. Dalakas stressed. "If dysphagia is not specifically tested, problems may remain hidden until the patient suddenly becomes aware of choking."
During the study, scientists examined swallowing among 32 patients randomly chosen from a larger group of post-polio patients. Using specialized imaging techniques, including videofluoroscopy and ultrasonography, they detected dysphagia in 31 patients — but only 14 were aware of this problem.
Typical signs of dysphagia included excessive tongue movements, a delay in the swallowing reflex and constriction of throat muscles, and uncontrolled flow of food from the mouth into the throat. These problems were often more severe on one side of the mouth and throat.
Dr. Dalakas and his colleague Barbara Sonies, Ph.D., of the National Institutes of Health also detected dysphagia using an index that assesses oral motor function based on 10 tests of muscle strength and motion, such as strength of tongue and lips, voice quality, and swallowing ability. "As the index score rises, the patient's risk of choking also goes up," Dr. Dalakas said. "Using this index, physicians can predict which patients are likely to choke."
Dr. Dalakas suggested that patients with post-polio syndrome visit their physician for a check of dysphagia and, in some cases, change eating routines to reduce choking risk. For example, patients with significant dysphagia should chew food on the less affected side, consume softer foods, use smaller bites when eating, and eat more slowly. He also recommended that family members or companions of such patients learn the Heimlich maneuver.
The exact cause of post-polio syndrome is unknown. During the first, acute polio infection, the virus destroys nerve cells that control limb and bulbar muscles. This causes symptoms that range from weakness to paralysis, depending on the number of nerve cells destroyed and how well the remaining, healthy neurons can compensate.
In post-polio syndrome, however, the compensating neurons become overworked and are no longer able to control muscles as effectively, Dr. Dalakas said. Post-polio syndrome may also be aggravated by the aging process, in which all individuals lose some neurons. In most individuals, half of the nerve cells controlling a muscle must die for weakness to result. Since the number of neurons is already abnormally low in post-polio patients, small additional losses can easily trigger muscle weakness.
"Studies of post-polio syndrome are rapidly advancing our knowledge of how motor neurons survive and endure and what causes them to dysfunction," said Murray Goldstein, D.O., M.P.H., NINDS director. "Thus, this research could have implications for other diseases that affect motor neurons — such as amyotrophic lateral sclerosis, or Lou Gehrig's disease, and the neuropathies. It may also help scientists to understand how aging affects the nervous system. "
The National Institute of Neurological Disorders and Stroke, one of the 13 National Institutes of Health in Bethesda, MD, is the primary supporter of brain and nervous system research in the United States.
* "Dysphagia in Patients with the Post-Polio Syndrome." Barbara C. Sonies, Ph.D., and Marions C. Dalakas, M.D. New England Journal of Medicine; April 25, 1991; pp. 82-91.
Last Modified December 28, 2012