Posted May 04, 2010 @ 08:53 AM
Posted May 04, 2010 @ 08:53 AM
Q: My grandmother had polio when she was little, but except for some mild weakness in her right leg she had gotten better. The doctors think she is coming down with it again. How can she have gotten polio again here in the U.S.?
A: This sounds like post-polio syndrome (PPS), and that is what I will discuss in today's column.
Poliomyelitis is caused by a virus that is shed in the stool of infected people. Poor sanitary conditions and poor hygiene contribute to its spread. After ingestion, the virus replicates in the nose/throat mucosa and/or the gastrointestinal tract of the patient. It then invades the lymph nodes and possibly spreads to the blood; in some cases it can also invade the neurons in the patient's brain and/or spinal cord.
About 90 percent to 95 percent of those infected with the polio virus have minor non-specific symptoms such as low-grade fevers, malaise, sore throat and/or headache, and these people recover with no problems. Some people also have GI symptoms such as nausea, vomiting and/or abdominal pain, and again typically have a full recovery.
About 1 percent of those infected develop paralytic polio (damage to muscle innervating neurons), causing muscle weakness (most often in one limb or on one side of the body) which can progress to flaccidity and paralysis. About half of these patients recover fully, a quarter have mild residual weakness and about a quarter have severe permanent disability. Overall, the prognosis is better for younger children.
Polio infection is definitively diagnosed by cultures of certain body fluids or blood antibody tests. The only treatment for polio is supportive care, but a 95 percent effective preventative vaccine exists and is routinely given to all children in the U.S. This not only helps prevent infection from the polio virus, but also helps eradicate the disease from the population since polio is only transmitted from person to person by the fecal-oral route discussed above.
From this discussion it should not be surprising that new cases of polio in the U.S. are essentially all contracted outside the country. In fact, worldwide vaccination programs are attempting to eradicate polio completely, as was done for smallpox.
Post-polio syndrome occurs in people years after they have had paralytic polio. One theory as to why PPS occurs is that the partially damaged neurons from the initial infection "wear out." This explains why there is no active viral infection in people with PPS, and why their symptoms are typically fatigue and slowly progressive muscle weakness affecting the same muscles as in the initial infection.
There is no specific test for PPS. In fact, it may be difficult to diagnose since the slow onset and subtlety of initial symptoms may be caused by many other conditions. The criteria to diagnose PPS are:
- A history of paralytic polio (even if there was an essentially complete recovery)
- A stable period after the initial infection, which can be decades long
- Gradual onset of persistent muscle weakness and sometimes muscle atrophy
- Symptoms that persist for over a year
- Other possible causes of the symptoms must be ruled out
PPS is actually pretty common in survivors of paralytic polio, affecting a quarter to half of these patients.
The slow progression of the symptoms, and the fact that they occur in a distribution that the patient survived in the past, make the prognosis for PPS good in the sense that it is rarely life threatening. However it can significantly impact the patient's quality of life.
Appropriate exercise to strengthen certain muscles to help offset the weakness from PPS can be beneficial in many patients; to date, no other treatments have been shown to be very effective.
Although new cases of polio are rare in the U.S., there are still about half a million Americans who are survivors of this disease (typically contracted before mass vaccination efforts helped minimize its occurrence) and, hence, are at risk for PPS; worldwide there are many millions of people at risk.
Although there is no known way to prevent PPS, regular exercise to keep muscles fit and strong as well as to stay healthy overall can help minimize the negative impact this condition may have.
Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at DrHersh@juno.com.
Clasificación Internacional de Enfermedades Codifico al Síndrome de Post Polio con el Código G14 Síndrome Postpolio Incluye : Síndrome postpoliomielítico Excluyéndolo del código B91Secuelas de poliomielitis