Post-polio syndrome (PPS, poliomyelitis sequelae) is a group of latent symptoms of poliomyelitis (polio), occurring in more than 80% of polio infections. The symptoms are caused by the damaging effects of the viral infection on the nervous system and typically occur 15 to 30 years <!-- (age 35 to 60) --> after an initial acute paralytic attack. Symptoms include decreasing muscular function or acute weakness with pain and fatigue. The same may also occur years after a nonparalytic polio infection.

The precise mechanism that causes PPS is unknown. It shares many features with myalgic encephalomyelitis/chronic fatigue syndrome, but unlike that disorder, it tends to be progressive and can cause loss of muscle strength. Treatment is primarily limited to adequate rest, conservation of available energy, and supportive measures, such as leg braces and energy-saving devices such as powered wheelchairs, analgesia (pain relief), and sleep aids.

Signs and symptoms

After a period of prolonged stability, some people who recover from polio infections begin to experience new signs and symptoms, characterised by muscular atrophy, weakness, pain, and limb fatigue. PPS is a very slowly progressing condition marked by periods of stability followed by new declines in the ability to carry out usual daily activities. Most patients become aware of their decreased capacity to carry out daily routines due to significant changes in mobility and decreasing upper limb function and lung capability. Fatigue is often the most disabling symptom; even slight exertion often produces disabling fatigue and can also intensify other symptoms.

Mechanism

Numerous theories have been proposed to explain post-polio syndrome. Despite this, no absolutely defined causes of PPS are known. The most widely accepted theory of the mechanism behind the disorder is "neural fatigue". A motor unit is a nerve cell (or neuron) and the muscle fibers it activates. Poliovirus attacks specific neurons in the brainstem and the anterior horn cells of the spinal cord, generally resulting in the death of a substantial fraction of the motor neurons controlling skeletal muscles. In an effort to compensate for the loss of these neurons, surviving motor neurons sprout new nerve terminals to the orphaned muscle fibers. The result is some recovery of movement and the development of enlarged motor units. The normal aging process also may play a role. Denervation and reinnervation are going on, but the reinnervation process has an upper limit where the reinnervation cannot compensate for the ongoing denervation, and motor unit loss occurs. What disturbs the denervation-reinnervation equilibrium and causes peripheral denervation, though, is still unclear. With age, most people experience a decrease in the number of spinal motor neurons. Because polio survivors have already lost a considerable number of motor neurons, further age-related neuron loss may contribute substantially to new muscle weakness. The overuse and underuse of muscles also may contribute to muscle weakness.

Another theory is that people who have recovered from polio lose remaining healthy neurons at a faster rate than normal. Little evidence exists to support this idea. Finally, the initial polio infection is thought to cause an autoimmune reaction, in which the body's immune system attacks normal cells as if they were foreign substances. Again, compared to neural fatigue, the evidence supporting this theory is quite limited.

In general, PPS is a diagnosis of exclusion whereby other possible causes of the symptoms are eliminated. Neurological examination aided by other laboratory studies can help to determine what component of a neuromuscular deficit occurred with polio and what components are new and to exclude all other possible diagnoses. Objective assessment of muscle strength in PPS patients may not be easy. Changes in muscle strength are determined in specific muscle groups using various muscle scales that quantify strength, such as the Medical Research Council (MRC) scale. Magnetic resonance imaging, neuroimaging, and electrophysiological studies, muscle biopsies, or spinal fluid analysis may also be useful in establishing a PPS diagnosis. Muscle strength and endurance training are more important in managing the symptoms of PPS than the ability to perform enduring aerobic activity. Management should focus on treatments such as hydrotherapy and developing other routines that encourage strength, but do not affect fatigue levels. but proves insufficient to recommend as a treatment. Joint instability can cause appreciable pain and should be adequately treated with painkillers. Directed activity, such as decreasing mechanical stress with braces and adaptive equipment, is recommended. PPS with respiratory involvement requires exceptional therapy management, such as breathing exercises and chest percussion to expel secretions (clearing of the lungs) periodically (monitored via stethoscope). Failure to properly assess PPS with respiratory involvement can increase the risk of overlooking an aspiration pneumonia (a life-threatening infection of the lower respiratory tract, especially so if not caught early on). Severe cases may require permanent ventilation or tracheostomy. Sleep apnoea may also occur. Other management strategies that show improvement include smoking cessation, treatment of other respiratory diseases, and vaccination against respiratory infections such as influenza.

Prognosis can be abruptly changed for the worse by the use of anesthesia, such as during surgery.

Epidemiology

Old data show PPS occurs in roughly 25 to 50% of people who survive a polio infection. Newer data from countries that asked their polio survivors show 85% of respondents have symptoms of post-polio syndrome. Typically, it occurs 30–35 years afterward, but delays between 8 and 71 years have been recorded. The disease occurs sooner in those with more severe initial infections. PPS is documented to occur in cases of nonparalytic polio (NPP). One review states late-onset weakness and fatigue occur in 14–42% of NPP patients.

See also

  • History of polio
  • List of polio survivors

<!-- already cited *Polio

  • Polio vaccine
  • Poliovirus -->

References

Further reading

  • Maynard, F.M., & Headley, J.H. (Eds.) (1999). Handbook on the Late Effects of Poliomyelitis for Physicians and Survivors. Saint Louis, MO: GINI (now Post-Polio Health International). Information on 90 post-polio topics; a compilation of the research and experience of over 40 experts.
  • March of Dimes Birth Defects Foundation. (1999). Identifying Best Practices in Diagnosis & Care. Warm Springs, GA: March of Dimes International Conference on Post-Polio Syndrome
  • Nollet F. "Perceived health and physical functioning in postpoliomyelitis syndrome". Vrije Universiteit Amsterdam, 2002.
  • Nollet, F. "Post-polio syndrome". Orphanet Ecyclopaedia, 2003
  • Silver, Julie K. (2001). Post-Polio Syndrome: A Guide for Polio Survivors and Their Families. New Haven: Yale University Press. (Dr. Silver is medical director, Spaulding-Framingham Outpatient Center; Assistant Professor, Department of Physical Medicine and Rehabilitation, Harvard Medical School.)
  • National Institute of Neurological Disorders and Stroke-Post-polio