History
Symptoms of postpolio syndrome (PPS) usually appear earlier in patients who have very severe residual weakness, individuals who had early bulbar respiratory difficulty in the acute illness, and persons who were older when they contracted acute polio. PPS symptoms tend to occur first in the weaker muscles.
Fatigue
In individuals without polio or PPS, the functional consequences of aging and loss of motor units may be unnoticeable until a very advanced age. In the individual with PPS, any further loss of strength may be more readily apparent. In contrast to patients with chronic fatigue syndrome, postpolio fatigue is prominent in the early hours of the afternoon and decreases after brief periods of rest and is exacerbated by minimal physical exercise. PPS-related fatigue usually does not prevent patients from working. Fatigue in PPS usually occurs on a daily basis, increases in severity as the day progresses, and is usually associated with physical weakness. [19, 20]
Fatigue in PPS is multidimensional. Different types of fatigue, such as general fatigue, physical fatigue, and mental fatigue, are determined by different variables. Potentially modifiable factors such as stress, depression, pain, and physical activity account for a portion of fatigue in PPS. [21]
Central pain pathogenesis can include chronic pain, type A personality, depression, dysfunctional reticular-activated system, sleep disorders, and respiratory dysfunction. PPS produces somnolence and difficulty in concentrating and remembering.
Peripheral pain pathogenesis may be metabolic exhaustion of the enlarged motor units, neuromuscular junction transmission defects, scarring within the motor neurons, or loss of motor units due to aging. PPS produces decreased muscular endurance and increased muscular fatigability.
A study by Romigi et al found a high prevalence of restless legs syndrome (RLS) in patients with PPS, with RLS possibly being a significant factor in fatigue. The investigators suggested that a link exists between neuroanatomic and inflammatory mechanisms in RLS and PPS. [22]
Muscle weakness
In PPS, muscle weakness and atrophy can be permanent, because of loss of motor units, or transient, because of muscle fatigue. [23, 24]
A number of functional etiologies for weakness have been hypothesized, including disuse, overuse, and chronic weakness, as well as weight gain.
Asymmetrical and scattered weakness may be present. Progression of muscle weakness is faster than in normal ageing. [25]
Some authors have found evidence that previously unaffected muscles later become weak; in these cases, they discovered that the patient was unaware of or had not been told that the particular muscle had been affected during the acute episode.
A systematic review conducted by Stolwijk-Swüste et al [26] concluded that the rate of decline in muscle strength in PPS is slow, and prognostic factors have not yet been identified. They suggested that long-term follow-up studies with unselected study populations and age-matched control individuals are needed to shed further light on this question.
Muscle pain
Deep aching pain may be a component of a myofascial pain syndrome or fibromyalgia. [10, 27]
This feature is extremely prevalent in PPS. Using a retrospective, cross-sectional survey, Stoelb et al investigated the frequency and most common sites of pain in patients with postpolio syndrome. [28] Pain symptoms were reported by 57 (90.5%) of the 63 study participants; pain was reported most often in the shoulders, legs, hips, and lower back, with the most intense pain occurring in the legs, knees, wrists, head, and lower back.
In a Swedish study, 68% of patients with PPS experienced pain at the examination. Pain was found to have a significant impact on their quality of life. [29]
Gait disturbance
Difficulty with gait is caused by progressive weakness, pain, osteoarthritis, or joint instability; it is common in patients who previously used assistive devices but later discarded them. The gait pattern of PPS patients is related to numerous intrinsic and extrinsic factors. [30] . Using 6-minute walk test, it was shown that walking speed was negatively correlated with the increased hip flexion, but not with the ankle plantar-flexion at foot-off in the patients with PPS. [31]
Respiratory problems
Respiratory disorders are most prevalent in patients with residual respiratory muscle weakness.
These changes cause chronic microatelectasis, diminished pulmonary compliance, increased chest wall tightness, chronic alveolar hypoventilation, decreased cough and expiratory flow, and decreased clearing of secretions.
The new respiratory difficulties are not only related to new respiratory muscle weakness but also to scoliosis, pulmonary emphysema, cardiovascular insufficiency, or poor posture.
A central component also may occur because acute bulbar polio often affects the medullary structures, including the reticular formation and sleep regulatory system.
Nonetheless, a study by Lira et al found that on spirometric evaluation, the only significant difference in lung function between patients with PPS and controls was an approximately 27% lower value in mean maximal voluntary ventilation. [32]
Swallowing problems (dysphagia)
Dysphagia can occur in patients with bulbar and nonbulbar postpolio.
Subclinical asymmetrical weakness in the pharyngeal constrictor muscles is almost always present in all postpolio muscular atrophy patients, including those who do not complain of new swallowing difficulties.
In one Finnish study of 51 people with PPS who were admitted to a rehabilitation center, 15 people reported daily problems with swallowing or voice production. The most commonly observed deficits in swallowing included decreased pharyngeal transit and food catching in the throat. [33]
Autonomic dysfunction
The cause is unclear; the peripheral component could include muscular atrophy and, therefore, diminished heat production.
Sleep apnea
This disorder is not uncommon in patients left with residual bulbar dysfunction or severe respiratory compromise. Patients with bulbar involvement had more frequent sleep apnea than patients without. They also had significantly more central apnea. [34]
Sleep apnea appears to be due to a combination of the following:
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Central apnea, due to a residual dysfunction of the surviving bulbar reticular neurons
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Obstructive apnea, due to pharyngeal weakness and increased musculoskeletal deformities from scoliosis or emphysema
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Postpolio muscular atrophy, resulting in diminished muscle strength of the respiratory, intercostal, and abdominal muscle groups
Restless legs syndrome
As previously mentioned, RLS is fairly common in people with postpolio syndrome. A study by Marin et al reported the prevalence of RLS to be 36% in the postpolio syndrome population, with the median severity, as measured using the Brazilian version of the International Restless Legs Syndrome Study Group (IRLSSG) severity score to be 23. In many patients, the onset of RLS and postpolio syndrome was concomitant. [35]
Flat-back syndrome
Another possible symptom in some patients with postpolio syndrome is the flat-back syndrome, which consists of the inability to stand erect because of forward flexion of the trunk and pain in the low back and legs. [36]
The flat-back syndrome typically occurs in patients with diminished lumbar lordosis as a result of instrumentation of the spine for scoliosis, vertebral fracture, or degenerative joint disease.
The trunk extensor musculature plays an essential role in maintaining upright posture, and it may be that PPS-related weakness in this musculature represents a major contributing factor to the flat-back syndrome in these patients.
Physical
In persons with postpolio syndrome, progressive weakness and atrophy may be observed in muscles that were affected initially by the poliovirus or in muscles that were spared clinically, which tends to happen in an asymmetrical distribution. Fasciculations sometimes can be observed in atrophic muscles, as a result of the lower motor neuron injury.
Obesity is widespread in postpolio survivors. A study by Chang indicates that the current body mass index (BMI) underestimates the total body fat mass percentage for those with poliomyelitis, leading the authors to suggest that a population-specific BMI should be used instead. [37]
