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Post-polio syndrome

From Academic Kids

Post-polio syndrome (PPS) (also properly but not commonly called post-polio sequelae) is a condition that can strike polio survivors anywhere from 10 to 40 years after their recovery from polio. PPS is believed to be caused by the death of individual nerve terminals in the motor units that remain after the initial polio attack. Symptoms include fatigue, slowly progressive muscle weakness, muscle and joint pain, and muscular atrophy. The severity of PPS depends only weakly upon how seriously the survivors were affected by the first polio attack. Doctors estimate the incidence of PPS at about 25 percent of the survivor population. There is no definitive test for PPS; diagnosis is accomplished primarily by identifying the symptoms and excluding other possible cause. Various laboratory studies (for example, magnetic resonance imaging (MRI), neuroimaging, electrophysiological studies, and muscle biopsies or spinal fluid analysis) may aid in the diagnosis.

At present, no treatment can cure or prevent PPS. Some experimental drug treatments, including pyridostigmine and seligiline, show promise in treating symptoms of the disorder. Doctors recommend that polio survivors follow standard healthful lifestyle practices: consuming a healthful diet, exercising in moderation, and visiting a doctor regularly.

PPS is a very slowly progressing condition that is marked by long periods of stability. PPS patients, compared with control populations, do not show any elevation in antibodies against the polio virus, and since PPS affects only certain muscle groups, doctors question whether the polio virus can cause a persistent infection in humans. Except in people with severe respiratory impairment, PPS is not usually life-threatening.

Scientists are studying a number of possible treatments for post-polio syndrome, including insulin-like growth factor (IGF-1) and other growth factors. Other researchers are looking at the mechanisms behind fatigue, and trying to tease out information from the brain, muscles, and neuromuscular junction (the site at which a nerve cell meets the muscle it helps activate). Scientists are also trying to determine if there is an immunological link in this disorder.

Causes

Several theories have been proposed to explain post-polio symptoms:

  • Neural fatigue: The most widely accepted theory is the "neural fatigue" one. Motor neuron fibers were originally damaged by the polio virus and were subsequently over-stressed because too few surviving neurons activated too many muscles. Eventually these neurons become fatigued and die, leading to the slowly advancing loss of muscle function that is typical of post-polio. This scenario may be accelerated by the fall-off in production of nerve growth factor (NGF) that occurs with menopause/andropause.
  • Mitochondrial disruption: This theory assumes that the major symptoms of PPS are a result of some interference with the action of mitochondria in the muscles and possibly the nerves. Failure of the mitochondria to produce sufficient energy would result in the muscle pain typical of PPS, and would, over time, cause muscle death (rhabdomyolysis) due to exerting the muscle beyond its ability to recover. The cause of this interference with mitochondrial action is presumably a change in the body's hormone balance, as mediated by the hypothalamus and other lower brain areas that control hormones (and which were, presumably, damaged by the original polio virus infection). As with the neural fatigue theory, menopause/andropause accelerates the process, though this time by most likely disrupting the NOTCH pathway that controls cell differentiation and damage repair.

One significant argument in favor of the mitochondrial disruption theory is that it more adequately explains the fatigue and cognitive difficulties ("brain fog") that usually accompanies post-polio.

  • Mechanical overwork: The stresses placed on nerves, muscles, and joints in a polio survivor are in many cases several times those experienced by other people. Problems with gait, in particular, can greatly overstress joints and the surviving muscles, and the polio surivior is also likely to compensate for weakened arms by jerking more when lifting/pulling something. Over time (and again with menopause/andropause), this results in fatigue and damage.
  • Reactivated polio: Though this theory has been largely discredited by laboratory studies that show no active polio virus in the body, there are still some people who believe that post-polio is caused by reactivation of latent polio virus in the body, similar to the way that shingles is a reactivation of the chicken pox virus.

In final analysis, it will likely turn out that post-polio symptoms are due to some combination of mechanisms.

Treatment

Treatment for post-polio is primarily palliative, as no reliable therapy to reverse symptoms is known. Palliative treatment includes:

  • Rest: Very often fatigue is the most disabling symptom of PPS, and many of those with the disease have discovered that by carefully managing energy expenditure they can prevent or reduce the worst fatigue episodes. Further, for many this "energy management" approach appears to reduce pain.

Though most authorities agree that rest is an important component of post-polio treatment, there is significant disagreement as to how much rest is necessary. Some hold that the best approach is to expend the absolute minimum amount of energy necessary to enjoy a reasonable lifestyle, while others feel that there is some threshold below which energy conservation is not helpful and may in fact be harmful (due to the general effects caused by lack of exercise).

  • Leg braces: Joint braces and other orthotics can reduce the stress on joints and, in some cases, muscles, and so may slow the progression of joint and muscle damage related to PPS. However, some authorities feel that many PPS patients rely on such items too much and for too long when they should be graduating to a wheelchair.
  • Wheelchairs: Wheelchairs (particularly powered wheelchairs) and "scooters" (small battery-powered vehicles) are useful both to conserve energy and to reduce the stress on weakened joints and muscles. Non-powered wheelchairs, however, are not generally recommended since they place too much stress on arm muscles and joints and may take too much energy to operate. In some cases even the scooters are not recommended since operating the "tiller" of the typical scooter can be tiring to arm muscles.
  • Surgery: In some cases surgery can be used to repair joint deformities, or to fuse joints (as in the back or ankle) that have become too weak.
  • Medications: Post-polio syndrome often causes significant levels of pain, sometimes in specific muscles or joints, and sometimes body-wide. Various forms of narcotic and non-narcotic pain-relievers, muscle relaxants, tranquilizers, and sleep medications may help to deal with the pain and related sleep problems.

Only a few non-palliative treatments for post-polio syndrome have shown any promise, and none have been subjected to any sort of rigorous clinical testing. There are, however, a few treatments that have developed some "following" in the PPS community:

  • L-carnitine: This amino acid has several functions in the body, one of the most important being the transport of fatty acids into the mitochondria. Researchers in Australia have had some success using doses of several grams per day.
  • Coenzyme Q10: CoQ10 is a general antioxidant, but it also plays a critical role in the function of the mitochondria, transporting electrons between the "complexes" that participate in the energy conversion cycle. A shortage of CoQ10 can cause the fatigue and muscle pain much like that experienced with PPS, and CoQ10 deficiency is especially likely if one is taking statin drugs to control cholesterol. Some PPS patients have reported significant improvements in their symptoms when taking several hundred milligrams of CoQ10 per day.
  • D-ribose: This "pentose" sugar is the "R" in RNA and a critical component of DNA, RNA, and enzymes. It is also a component of ATP, the energy-transporting molecule produced by the mitochondria. A shortage of d-robose can produce fatigue and muscle pain. Some PPS patients have reported significant improvement in pain and fatigue symptoms when taking on the order of 20 grams/day of d-ribose.
Based in part on http://www.ninds.nih.gov/health_and_medical/disorders/post_polio_short.htm

See: "The Polio Paradox" by Dr. Richard Bruno, Director of The Post-Polio Institute in Englewood, New Jersey

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