Post-polio syndrome is a condition that frequently affects survivors of poliomyelitis, a viral infection of the nervous system. Typically the symptoms appear 20-40 years after the original infection, at an age of 35 to 60. Symptoms include new or increased muscular weakness, pain in the muscles, and fatigue.
Post-polio patients are also often noted to have memory problems, various cognitive difficulties, and an increased sensitivity to anesthetics. Weight gain is also a frequently noted symptom, though it's hard to tell if this is due to the disorder directly or due to the decreased level of physical activity that usually accompanies the disorder.
Fatigue is often the most disabling symptom, as often even slight exertion can produce disabling fatigue and also increase other symptoms.
Diagnosis of post-polio syndrome can be difficult, since the symptoms are hard to separate from the original symptoms of polio and from the normal infirmities of aging. There is no laboratory test for post-polio syndrome, nor is there any other specific diagnostic, so diagnosis is usually a "diagnosis of exclusion" were other possible causes of the symptoms are eliminated.
The precise mechanism that causes post-polio syndrome is unknown. It shares many features in common with myalgic encephalitis, a form of chronic fatigue syndrome that is apparently caused by viral infections, but unlike those disorders it tends to be progressive, and can cause tangible loss of muscle strength.
One theory of the mechanism behind the disorder is that it is due to "neural fatigue" from overworked neurons. The original polio infection generally results in the death of a substantial fraction of the motor neurons controlling skeletal muscles, and the theory is that the remaining neurons are thus overworked and eventually wear out.
Another theory holds that the original viral infection damages portions of the lower brain, possibly including the thalamus and hypothalamus. This somehow upsets the hormones that control muscle metabolism, and the result is a metabolic disorder similar to mitochondrial disorder that causes muscle pain and injury (via rhabdomyolysis) and also causes the fatigue.
Treatment generally is limited to supportive measures, primarily leg braces and energy-saving devices such as powered wheelchairs, plus pain relievers, sleep aids, etc. However, some post-polio patients claim to have found significant relief using large amounts of various food supplements, primarily l-carnitine, CoQ10, and d-ribose.