PSN Library Files

Management of post-polio syndrome

Daria A. Trojan*, Lois Finch

Department of Neurology, Neurosurgery, and Physiotherapy

Montreal Neurological Institute and Hospital

McGill University

3801 University Street

Montreal, Quebec, H3A 2B4, Canada

NeuroRehabilitation 8 (1997) 93-105

Lincolnshire Post-Polio Library copy by kind permission of Dr. Trojan

Abstract

Many patients with post-poliomyelitis syndrome can benefit from a management program. When a post polio patient presents with new symptoms, it is first essential to identify and treat other medical and neurological conditions which could produce these symptoms. New weakness can be managed with exercise (stretching, strengthening, and aerobic), avoidance of muscular overuse, weight loss, orthoses, and assistive devices. Fatigue can be managed with energy conservation techniques, lifestyle changes, pacing, regular rest periods or naps during the day, amitriptyline to improve sleep, and possibly pyridostigmine (trial in progress). The management of pain is dependent upon its cause. The treatment of post-polio muscular pain can include activity reduction, pacing (rest periods during activity), moist heat, ice, and stretching, use of assistive devices, and life style modifications. Fibromylagia can be treated with amitriptyline, cyclobenzaprine, and aerobic exercise. Joint and soft tissue abnormalities can be managed with modification of extremity use, physiotherapy, orthoses, assistive devices, non-steroidal anti inflammatory medications, and rarely steroid injections and surgery. Superimposed neurological disorders may produce pain, and should be identified and treated. The identification and treatment of pulmonary dysfunction in a post-polio patient is an important aspect of management, and is discussed elsewhere in this issue. Dysphagia can be managed with diet changes, use of special breathing and swallowing techniques, monitoring fatigue and taking larger meals earlier and smaller meals later, and avoiding eating when fatigued. The management of psychosocial difficulties usually requires an interdisciplinary approach, and may include a post-polio support group, social worker, psychologist, and psychiatrist. © 1997 Elsevier Science Ireland Ltd.

Keywords: Poliomyelitis; Rehabilitation; Exercise; Treatment

*Corresponding author. Tel.: + 1 514 3988911; fax: +1 514 3987371.

1053-8135/97/$17.00 © 1997 Elsevier Science Ireland Ltd. All rights reserved.

PII S 1053-8135(96)002 1 4-4

1. Introduction

Although currently there is no specific treatment for post-poliomyelitis syndrome (PPS), patients with this condition can be managed with a resultant improvement [1]. Many patients can benefit from at least some of the measures described below. Because of the great variety of symptoms reported by PPS patients, an interdisciplinary approach to management is most effective. The team can include physicians such as a primary care physician, physiatrist, neurologist, pulmonary specialist, psychiatrist, orthopedist, and rheumatologist. Other health personnel who are frequently involved in the care of these patients are a physical therapist, occupational therapist, psychologist, social worker, dietician, and orthotist. Table 1 summarizes the management approach in PPS.

Because there is currently no diagnostic test for PPS, this syndrome is diagnosed by excluding other medical and neurological disorders which can produce similar symptoms. In addition, the symptom of fatigue is extremely common even in the general population, and may be caused by a variety of disorders. There are also many potential causes for pain and weakness. The differential diagnosis is discussed in a separate article in this issue. It is very important that these other causes be identified and treated first before new symptoms in a post-polio patient can be attributed to PPS.

In a post-polio patient presenting with complaints of new weakness, fatigue, and/or pain, we recommend that a thorough medical and neurological examination, with screening blood tests be performed first. Laboratory tests can include CBC, SMAC (Na, K, Cl, HCO₃, glucose, BUN, Cr, calcium, phosphorus, magnesium, total protein, albumin, total bilirubin, ALT, AST, LDH, alkaline phosphatase, creatinine kinase), TSH, ESR, and serum protein electrophoresis. Some investigators [2] recommend that standard electromyography (EMG)/nerve conduction studies be performed in all four extremities on virtually all patients to confirm evidence for previous motor neuron loss and to exclude peripheral nerve dysfunction, and other neuropathic and myopathic conditions. We recommend performing EMG studies in those patients who have an unclear history of previous paralytic polio, or who lack the usual findings of previous polio on physical examination. Other studies such as nerve conduction studies, F-waves, H reflexes, can be performed when clinically indicated to rule out other neurological disorders. This is especially true for those patients who present with complaints of numbness, and/or sensory deficits on neurological examination. Radiographic studies such as plain X-rays are frequently needed to evaluate joint dysfunction. In addition, CT scans and/or MRIs may also be needed to exclude conditions such as spinal stenosis, radiculopathy, and cervical myelopathy. In general, EMG is not helpful in excluding these conditions in patients with past paralytic polio because of the changes present as a result of previous polio. Pulmonary function tests (PFTs) should be performed in virtually all patients because unexpected deficits can be present even in those patients without a history of previous or recent respiratory dysfunction. Sleep studies may be necessary in those patients with symptoms suggestive of sleep apnea (snoring, frequent waking, daytime fatigue, morning headaches, impaired cognition, irritability, anxiety, cyanosis, and depression). Swallowing studies with videofluoroscopy may also be necessary.

Table 1 Management of post-polio syndrome (PPS)

1. Identification and treatment of other medical and neurological disorders which can mimic the

symptoms of PPS.

2. Management of weakness

Strengthening exercises (isometric, isotonic, isokinetic)

Aerobic exercise

Stretching exercises to decrease or prevent contractures

Avoidance of muscular overuse

Weight loss

Orthoses

Use of assistive devices

3. Management of fatigue

Energy conservation techniques

Lifestyle changes

Pacing

Regular rest periods, naps during day

Amitriptyline to improve sleep

Possibly pyridostigmine (trial in progress)

4. Management of pain
5. Post-polio muscular pain, muscular cramps, muscular pain with activity

Activity reduction

Pacing (rest periods during activity)

Moist heat, ice, and stretching

Use of assistive devices

Life style modifications

1. Fibromyalgia

Amitriptyline

Cyclobenzaprine

Aerobic exercise

1. Joint and soft tissue abnormalities

Modification of extremity use

Physiotherapy for use of physical modalities, strengthening, stretching.

Orthoses

Assistive devices

Non-steroidal anti-inflammatory medications

Steroid injections

Surgery

1. Treatment of other superimposed neurologic disorders (e.g. carpal tunnel syndrome, radiculopathy, spinal stenosis).
2. Pulmonary disfunction

Preventive measures (pneumococcal vaccine, yearly influenza vaccine)

Ventilatory assistance (non-invasive methods preferred)

Identification and treatment of sleep apnea

Glossopharyngeal breathing

6. Dysphagia

Changing or restricting diet

Use of special breathing techniques

Use of special swallowing techniques

Monitoring fatigue, and taking larger meals earlier, and smaller meals later

Avoiding eating when fatigued

7. Psychosocial difficulties

Interdisciplinary approach

Post-polio support group

Evaluation and treatment by social workers, psychologists, psychiatrists.

2. Management of weakness

The management of new weakness in a postpolio patient can include a strengthening exercise program, an aerobic exercise program, stretching to decrease or prevent contractures, avoidance of muscular overuse (exercising to the point of muscle pain and fatigue), weight loss, bracing, and use of assistive devices. For more detailed information on muscular function and exercise in postpolio patients, please refer to the article on this topic in this issue.

Exercise in post-polio patients has been a controversial topic for many years, primarily because of case reports of overwork weakness in these patients [3,4]. These clinical findings were supported by studies in denervated muscles of rats [5-8]. However, more recently, several studies have found that exercise can result in an increase in strength in post-polio patients many years after the acute illness. Feldman and Feldman and Soskolne [9,10] were the first to report in more recent years the beneficial effects of an exercise program many years after polio. Since then several other studies have confirmed their finding of the benefical effects of an isotonic strengthening exercise program [11,12] as well as isokinetic and isometric strengthening exercise programs [12-14]. In addition, fiber density, jitter, blocking, median macro-electromyography motor unit potential amplitude, and creatinine kinase were not changed significantly with the exercise program [12]. In addition to strengthening exercise, aerobic exercise has also been found to be beneficial in post-polio patients. Jones et al. [15] found that the average level of aerobic fitness in post-polio patients was 5.6 METS, or similar to that seen in patients just after a myocardial infarction. Aerobic exercise both in the upper and lower extremities on a bicycle ergometer [15-17], and on a treadmill [18] has been shown to be helpful. The bicycle ergometer training programs resulted in similar training effects to those observed in normals with improved maximum oxygen consumption, duration of exercise, watts attained during exercise, and maximum expired volume per unit time. Treadmill training resulted in improved economy or energy cost of walking, and thus walking duration, but no change in cardiorespiratory conditioning.

Thus, exercise has been shown to be beneficial in post-polio patients, even in muscles where new weakness has been reported. The exact exercise prescription is dependent on a number of factors. Isometric exercise is most useful in muscles with less than 3 strength (MRC scale), or in muscles over a painful joint. An isotonic exercise program is most useful in muscles with grade 3 or better strength, and without a painful joint. Isokinetic exercise could also be used when equipment is available. An aerobic

exercise program such as using a bicycle ergometer, walking, or swimming can also be useful, but preferably should be an activity which the patient enjoys to increase compliance. A warm-up and cool down period with stretching exercises should be included [2]. Some patients can also benefit from more agressive stretching of contractures (if no contraindications exist), such as knee flexion contractures and ankle plantarflexion contractures to improve gait and stability. Early in the exercise program, it is best for patients to be monitored carefully, to ensure that the exercise prescription is being followed correctly and that overuse of muscles and joints is not occurring. Once the patient understands the exercise program well, and can self-monitor, less frequent follow-up such as every few months is reasonable [19].

Even though several different types of exercise have been shown to be beneficial in the late post-polio patient, exercise should be used judiciously, and should be avoided completely in some patients. Muscle groups which are being overused may benefit from rest or supportive devices such as braces. In addition, these studies have not assessed the effect of exercise programs on patient function and general well-being, and the long term effects of exercise in these patients are still unclear.

Overuse of muscles must be avoided in postpolio patients. Muscular overuse in patients with past paralytic polio was thought to be the cause of increased weakness in several case reports [3]. This new weakness may be permanent. Perry et al. [20] performed dynamic electromyography during gait in 34 PPS patients, and found evidence for overuse (compared to normals). The usefulness of creatinine kinase levels in the monitoring of overuse in post-polio patients is unclear, however Waring and McLaurin [21] found a significant correlation between CK levels and distance walked during ambulatory activities in the previous 24 h, indicating that CK could be a marker of overuse. In addition, in one case report [22], CK was found to be markedly elevated in a post-polio patient with symptoms of weakness, fatigue, and pain. With a reduction in exercise, serum CK levels decreased and symptoms resolved.

Waring et al. [23] completed a retrospective study of lower extremity orthotic management for ambulation in 104 post-polio clinic patients, and found that 78% of patients noted that appropriate orthotic prescription subjectively improved ability to walk, increased perceived walking safety, and reduced pain. Clark et al. [24] have described some of the more common biomechanical deficits and their orthotic management in post-polio patients.

These include inadequate dorsiflexion in swing, dorsiflexion collapse in stance, genu recurvatum (knee hyperextension), genu valgum (valgus deformity at the knee), and mediolateral ankle instability. In some patients, strengthening exercises can be tried first to control these deformities. If this is impossible, impractical, or not useful, orthoses can be used. For example, inadequate dorsiflexlon occurs secondary to·weakness of ankle dorsiflexors, and results in a foot drop, and a tendency to fall or trip. This problem can be treated with an ankle-foot-orthosis (AFO). Genu recurvatum is a common deformity in post-polio patients and is usually caused by quadriceps weakness, with a resultant tendency of the patient to ‘lock’ the knee to improve stability of the lower extremity. This deformity can cause pain and decreased efficiency of ambulation secondary to an increase in movement at the knee during gait. Genu recurvatum can be managed with an AFO, knee orthosis, or in patients with more severe weakness (Medical Research Council 3 or less), a knee ankle foot orthosis (KAFO) may be necessary. For further information on orthotic management, please refer to the appropriate article in this issue. In addition to orthoses, other assistive devices which can be useful for post-polio patients to improve mobility and safety are canes, crutches, manual wheelchairs, electric wheelchairs, and motorized scooters.

3. Management of fatigue

Excessive fatigue in PPS patients can be managed with the use of energy conservation techniques, life style changes, pacing, and taking regular rest periods or naps. Tricyclic antidepressants have been reported

to reduce fatigue, possibly by improving sleep, or by other more direct effects on central neurotransmission [2]. The anticholinesterase pyridostigmine may be useful, and a multicentered trial of this medication in PPS is currently in progress (see below).

Energy conservation techniques can include discontinuing some unnecessary energy-consuming activities (e.g. making a bed), using a handicap license plate, seating and workstation corrections, sitting instead of standing, moving the location of certain items and supplies to make them more easily accessible (e.g. washer and drier on first floor and not in basement), and using an electric scooter for longer distances. To reduce shoulder strain, driving wheel positions can be changed and mobile arm supports can be attached to wheelchairs, desks, or tables [25]. Life-style changes may include discontinuing certain activities such as volunteer work, changing to a more sedentary employment, or working part-time. Regular naps during the day, especially in the early afternoon, can be beneficial in the management of general fatigue, and patients (even working patients) should be encouraged and assisted to do this.

Agre and Rodriguez [26] found that pacing was helpful for muscular fatigue. Seven symptomatic post polio patients were studied on three separate occasions at least 1 week apart with three different exercise protocols. Patients, when allowed to take regular rest periods during an isometric endurance test of the quadriceps at 40% maximum voluntary contraction (MVC), were found to have less local muscle fatigue, increased work capacity, and improved recovery of strength after activity. Therefore, regular rest periods during activity can result in improved work capacity and should be encouraged.

A dilemma exists in the management of fatigue because neither medical personnel nor patients have means other than symptomatology with which to measure their activity or exercise level. Because patients with past poliomyelitis can perceive exertion at the peripheral muscular level during activity in a fashion similar to non-polio control groups [27], they should be taught to attend to their perception of exertion and to monitor fatigue [28]. The Borg Rating of Perceived Exertion (RPE) [29] is a useful measure which can be used to judge effort (Fig. 1). This 15 point scale with verbal anchors progressing from 6 at the lowest level, or light; to 20 at the highest, or very, very, hard level was originally developed for cardiac patients. It is an indicator of physical strain integrating peripheral muscle, joint, and cardiorespiratory signals that correlates well with heart rate (r=0.90), blood pressure [30], and blood lactate levels (r=0.83) [31]. The RPE is routinely used as a limit of exercise capacity in other conditions [32], and has been used more recently in PPS [18,33]. PPS individuals, after one training session, reliably (r=0.83) used the RPE in an exercise test to monitor their effort and finish the test [33]. This ability to use and understand the safe levels of exertion improves with intensity of activities and practise. Because the level of exertion can be reliably identified with the RPE in a PPS population, it can be used as the point at which to end any daily activity or exercise regime. Through the use of a daily/weekly diary with the RPE to identify levels of fatigue, patients can select their own appropriate level and pace their everyday activities. An RPE level 14, with the anchor word ‘hard,’ is the top level of exertion recommended. RPE levels with anchor words are more reproducible [34] and level 14 has been used in other exercise limiting cases [18,33]. Clear and early identification of fatigue, either at a local muscular level from exercise, or at a global body fatigue level from daily activities, by using RPE level 14 allows PPS patients to develop training strategies to prevent or reduce injury and overuse syndromes.

Fig. 1. The Borg scale of perceived exertion. The original Borg scale of

perceived exertion has been modified. The numbers from 6 to 10 are in green,

the numbers from 11 to 15 are in yellow, and the numbers from 16 to 20 are

in red, similar in concept to traffic lights. A figure has been added for each

colored area to depict the amount of effort represented by the numbers and

anchor words. Reprinted with permission from the Scandinavian Journal of

Rehabilitation Medicine [29]. The range discrepancy between the colour

scales (green and yellow) as marked in the figure and as detailed in this

description, existed in the published article. Lincolnshire Post-Polio Library

Administration.

4. Management of pain

Pain in post-polio patients can occur from a variety of causes. Management of pain is thus dependent upon the etiology. Pain can be caused by muscular abnormalities, joint and soft tissue abnormalities, and other superimposed neurological abnormalities. Overuse is the most likely etiology of many of the pain

syndromes. The location of pain appears to be dependent upon the method of locomotion [35]. In their study, Smith and McDermott [34] showed that pain in the lower extremities and lower back occurred more frequently in ambulatory patients, whereas pain in the upper extremities tended to occur more frequently in those patients who used wheelchairs or crutches.

Common muscular causes for pain include a ‘post-polio muscular pain,’ [2], muscular overuse, muscular cramps, fasciculations, and fibromylagia [36]. ‘Post-polio muscular pain’ typically occurs in muscles previously affected by polio, and is usually described as an aching sensation similar to that experienced at the time of paralytic polio. It usually occurs at the end of the day, and is aggravated by activity [2]. Patients can also experience a muscular pain with activity. Painful muscular cramps can occur either with activity or at the end of the day. Muscular cramps and muscular pain with activity are probably secondary to overuse, and should be avoided. Management of these types of pain include reduction of activity, taking rest periods during activity (pacing), use of moist heat and stretching, use of assistive devices, and lifestyle modifications. Fasciculations are a sign of previous motor neuron damage, and are reported by patients with previous paralytic polio. Fibromyalgia occurs commonly in patients presenting to a post polio clinic and can be treated with amitriptyline, cyclobenzaprine, aerobic exercise, and other measures [36].

Joint and soft tissue abnormalities include osteoarthritis, tendinitis, bursitis, ligamentous strain, joint deformities, and failing joint fusions. Because of residual weakness from paralytic polio, post-polio individuals may chronically use certain joints and extremities in abnormal ways which may predispose them to injury of joints, tendons, bursae, and ligaments. The resultant mechanical stresses and abnormal postures may perpetuate the pain problem. In a cross-sectional study of 61 post-polio patients, the prevalence of radiographically determined moderate to severe osteoarthritis of the hand and wrist was 13%, but the prevalence of mild osteoarthritis in the same joints was 68%. Associated factors for mild osteoarthritis were age greater than 50, lower extremity weakness, high current locomotor disability, and high current usage of assistive devices [37]. In addition, abnormal forces around joints may also produce joint deformities such as genu recurvatum, and genu valgum. Many of these causes for pain are treatable. Treatments can include modification of extremity use, physiotherapy for use of physical modalities [e.g. ice, superficial heat, ultrasound, transcutaneous electrical nerve stimulation (TENS)], strengthening, orthoses to control joint deformities and failing joint fusions, assistive devices, non-steroidal anti inflammatory medications, acetominophen, and rarely steroid injections or surgery. Stretching of tight tendons and soft tissues may be helpful. However, some contractures may be biomechanically beneficial for the patient, and these should not be stretched [38,39].

Superimposed neurological disorders which can cause pain include peripheral neuropathies, radiculopathies, and spinal stenosis. Electromyographic findings in 100 consecutive post-polio patients revealed a high prevalence of carpal tunnel syndrome (35%). Other neuropathies which were found included ulnar neuropathy at the wrist (2%), peripheral neuropathy (3%), carpal tunnel syndrome and ulnar neuropathy (3%), brachial plexopathy (1%), radiculopathy (4%), and tibial neuropathy (1%) [40]. Werner et al. [41] found that the use of assistive devices is a major risk factor for carpal tunnel syndrome in post-polio patients. Treatments for carpal tunnel syndrome can include splinting [42], use of pads on canes or crutches, or use of a special grip for canes and crutches which places the wrist in a more neutral position, and increases the weight-bearing surface of the hand [2]. For patients with lumbo-sacral radiculopathies or low-back pain, use of lumbosacral corsets, shoe lift, back supports, or pelvic supports can be helpful. Spinal stenosis can be treated with exercise, use of a cane, TENS, and a lumbosacral orthosis. In some cases, surgery may be necessary.

Pulmonary dysfunction

Symptoms of respiratory dysfunction are common in patients with past paralytic polio [43]. Compromised lung function can occur in postpolio individuals irrespective of whether or not shortness of breath is present [44]. Respiratory compromise occurs primarily in those individuals who required ventilation at the time of acute polio, but may also occur in those who do not report previous respiratory involvement. Risk factors for respiratory compromise greater than 35 years after acute polio are the need for ventilation at acute polio and age at acute polio of greater than 10 years [44]. Manifest hypoventilation is rare in post polio patients, and was reported to be present only in 2 of 40 post-polio patients who had respiratory and non-respiratory poliomyelitis at least 30 years previously [45]. However, many of the 87.5% of those who were initially weaned from a respirator may again require the use of a respirator [46]. Respiratory muscle weakness is the main cause of respiratory insufficiency in post-polio patients, however other contributing or causal factors include central hypoventilation due to previous damage from bulbar poliomyelitis [47], scoliosis and kyphosis, sleep disordered breathing, obesity, other pulmonary diseases, smoking, and cardiac disease.

Sleep apnea is a common problem in post-polio patients, and may be central, obstructive, or both [48]. This condition is important to diagnose since if untreated, it can eventually result in acute cardiopulmonary failure [49]. Please refer to the article on pulmonary dysfunction in this issue for further details on this topic, sleep apnea, and the management of both conditions.

6. Dysphagia

Symptoms of swallowing dysfunction are less common in post-polio patients than the other difficulties mentioned above, however they can occur in 10-20% of selected samples of post-polio patients [50]. Dysphagia can occur in patients with a previous history of bulbar poliomyelitis, but can also occur in post polio patients without previous bulbar involvement. In addition, mild to moderate abnormalities may be found on videofluoroscopy regardless of whether or not the patient is symptomatic [51,52]. Symptoms can include food sticking, coughing or choking during eating, and slowing of swallowing and eating [50]. Post-polio dysphagia is most commonly due to weakness of pharyngeal or laryngeal muscles. In patients who are complaining of swallowing or feeding dysfunction, a videofluoroscopic swallowing evaluation should be performed, preferably with a swallowing therapist. Videofluoroscopic abnormalities can include unilateral bolus transport, pooling in the valleculae or pyriform sinuses, delayed pharyngeal constriction, impaired tongue movements, and rarely aspiration [51]. However, it must not be assumed that all dysphagia in post-polio patients is secondary to polio, but other abnormalities such as structural lesions should also be ruled out. In one study [53], 20 patients with past polio and dysphagia were evaluated with cinefluoroscopy. Other abnormalities not necessarily secondary to polio were found and included a short stricture (one patient), a Zenker diverticulum (one patient), bilateral pharyngeal pouches (five patients), and unilateral pouch (one patient). In addition, laryngeal dysfunction may contribute to dysphagia. In one study [54], the laryngeal function of 9 of 21 post-polio patients with swallowing complaints was studied, and all nine patients had some degree of abnormality on laryngeal videostroboscopy. Symptoms of dysphagia and videofluoroscopic abnormalities appear to progress with time [51,55]. Management of dysphagia in a post-polio patient can include changing or restricting the diet to certain ‘safe’ substances such as purees or thickened liquids (preferably as determined by videofluoroscopy), use of special breathing techniques, use of special swallowing techniques such as turning the head to one side, monitoring fatigue and taking larger meals earlier and smaller meals later, and avoiding eating when fatigued [2,50].

7. Psychosocial difficulties

Post-polio patients who are now faced with PPS may have great difficulty adjusting to this second and

unexpected disability. Many of these patients have had to come to terms with the residua of a severe childhood illness, and now they are being asked to once again deal with polio-related difficulties. Because polio is now considered to be a ‘conquered disease,’ patient problems are compounded by the general lack of knowledge among the medical profession about both acute polio and PPS [56].

Some investigators have described a ‘polio personality,’ and have suggested that this may actually contribute to post-polio sequelae [57,58]. Polio survivors tend to be well-educated, competent, hard driving individuals who demand perfection both from themselves and others around them [2,59]. In a survey conducted by Bruno and Frick [57], 676 polio survivors were recruited by sending out 1200 questionnaires to post-polio clinics and support groups in the US. The mean type A score was found to be significantly higher in this post-polio group than in a previously reported non-disabled control group. In addition, type A score was significantly higher in those with muscle pain and fatigue. Despite their difficulties, polio survivors have more years of formal education and a larger proportion are married than the general disabled and non-disabled populations. In addition, they have higher levels of employment than the general disabled population [59].

Frick [56] suggested that individuals with PPS may experience personal devaluation, isolation, and depression as psychological responses. In one study [60], the Symptom Check List-90 (SCL90R), Psychosocial Adjustment to Illness ScaleSelf Report (PAIS-SR), and questionnaire about polio histories was administered to 93 individuals with a past history of polio (71 from a post-polio clinic and 22 recruited from a post-polio support group). Results indicated psychologic distress. Elevated SCL-90R scores in men occurred in somatization, depression, anxiety, hostility, and phobia. In women, elevated scores occurred in somatization, depression, anxiety, and psychoticism. In another study [61], in which 116 polio survivors were recruited from a polio registry, the prevalence of depression and distress was found to be 15.8%. Psychological distress/depression was correlated with physical symptoms. The emotional responses to a new disability may pose difficulties for the treatment of these patients. Patients may resist making the necessary changes in their life to effectively manage their new difficulties.

Treatment of psychosocial difficulties related to PPS is best managed with an interdisciplinary approach. It may include obtaining help from a post-polio support group, and evaluation and treatment by health professionals such as psychologists, social workers, and psychiatrists.

8. Drug trials and pharmacotherapy

Several small clinical trials of pharmacological treatments have been completed in PPS patients. Pyridostigmine (Mestinon) 180 mg per day has been evaluated in an open trial using an objective measure of neuromuscular junction transmission (jitter as measured by stimulation single fiber electromyography) in 17 patients by Trojan et al. [62]. A significant relationship between subjective fatigue response to pyridostigmine and improvement in neuromuscular junction transmission with edrophonium (a short acting anti-cholinesterase similar to pyridostigmine) was found. This suggests that fatigue in PPS is due to anticholinesterase-responsive neuromuscular junction transmission deficits in at least a proportion of patients (Fig. 2). In addition, Seizert et al. [63] have found improvements in some objective measures of strength and subjective measures of fatigue with pyridostigmine 180 mg per day in a double-blinded, placebo-controlled, crossover trial in 27 PPS patients. Because of these encouraging preliminary results, a multicentered trial of this medication is currently underway.

Amantadine and high dose prednisone have also been assessed in PPS. Stein et al [64] randomly assigned 25 PPS patients with fatigue to amantadine 100 mg twice a day or to placebo for 6 weeks. Fatigue level was assessed with the Fatigue Severity Scale, and Visual Analog Scale for Fatigue. No association was found between amantadine and clinical response to fatigue, although 54% of amantadine patients, and

43% of placebo patients reported improvement in fatigue. Dinsmore et al [65] studied the effect of high dose prednisone in 17 PPS patients (with new muscle weakness). Patients were randomly assigned either to prednisone (80 mg per day for 28 days, followed by a gradual reduction) or placebo. Outcome assessments included measures of isometric strength by a modified Tufts Quantitative Neuromuscular Examination (TQNE) [66], manual muscle testing, and subjective fatigue assessment. There were no significant differences between groups in terms of muscular strength and subjective fatigue. Another medication which may warrant further study is deprenyl (selegiline), a neuroprotective agent. In a report of two cases [67], deprenyl was found to produce an improvement in PPS symptoms, and this improvement ceased with discontinuation of the drug. Thus, several potential pharmacological treatments have been evaluated in PPS, and of these pyridostigmine appears to be most promising.

Other potential treatments which could be evaluated in PPS in the future include other neuroprotective agents such as vitamin E, and neurotrophic factors such as insulin-like growth factor (IGF-1), and brain derived neurotrophic factor (BDNF).

FIGURE 2 Graph

Fig 2. Reduction of fatigue with pyridostigmine is associated with reduction

of jitter (on stimulation single fiber electromyography) with edrophonium

injection. Jitter is a measure of neoromuscular junction transmission

adequacy, and is abnormally increased in post-polio patients. Pyridostigmine

responders (open circles) are those who report a reduction in fatigue with pral

pyridostigmine 180 mg per day. Pyridostigmine non-responders are illustrated

with closed circles. Jitter plots are normalized to 100% of pre-edrophonium

mean jitter. A significant difference in jitter means is observed with

comparison of pyridostigmine-responders (n=9) before and after

edrophonium injection (Bonferroni corrected, P < 0.0001). A significant

difference is also observed between pyridostigmine-responding and non

responding patients (n=8), after edrophonium injection (P < 0.001). There is

no significant difference in jitter means of pyridostigmine-non-responders

before and after edrophonium injection (P > 0.8). Error bars=SEM. Reprinted

from the Journal of the Neurological Sciences [62], with kind permission of

Elsiver Science — NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The

Netherlands.

9. Summary

Other medical and neurological causes of new symptoms in a post-polio patient should be identified and treated before attributing new difficulties to PPS. Many patients with PPS can benefit from an interdisciplinary, individualized, management program which is dependent upon the specific symptoms. This program can include pacing with regular rest periods and naps, avoidance of overuse, judicious exercise, orthotics, assistive devices, energy conservation techniques, and life style changes.

Acknowledgements

Parts of this manuscript were reprinted with permission from Milestone Medical Communications, A Division of Ruder-Finn, from a disease management monograph entitled ‘Current Trends in Post Poliomyelitis Syndrome’ (1996). This work was supported in part by the Fonds de la recherche en sante du Quebec, and the Association Polio Quebec. We are indebted to Dr. Neil Cashman for his constructive criticism in the preparation of this manuscript.

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This article is part of a collection of post-polio related articles that appeared together in one issue of NeuroRehabilitation. A number of those articles are available in the Lincolnshire Post-Polio Library. See NeuroRehabilitation 8 (1977)

Pathophysiology and diagnosis of post-polio syndrome Daria A. Trojan*, Neil R. Cashman

Department of Neurology and Neurosurgery

Montreal Neurological Institute and Hospital

McGill University

Montreal, Quebec, Canada

NeuroRehabilitation 8 (1997) 83-92 Lincolnshire Post-Polio Library copy by kind permission of Dr. Trojan

Abstract

Post-poliomyelitis syndrome is defined as a clinical syndrome of new weakness, fatigue and pain which can occur several decades following recovery from paralytic poliomyelitis. The cause of this disorder is still unclear, and many possible etiologies have been proposed. The most widely accepted etiology was

first proposed by Wiechers and Hubbell, which attributes PPS to a distal degeneration of massively enlarged post-polio motor units. Other probable contributing factors to the onset of this disease are the ageing process, and overuse. Currently, there is no specific diagnostic test for PPS, which continues to be a diagnosis of exclusion in an individual with symptoms and signs of the disorder. © 1997 Elsevier Science Ireland Ltd.

Keywords: Poliomyelitis; Diagnosis; Pathophysiology

*Corresponding author. Tel.: + 1 514 3988911; fax: +1 514 3987371.

1053-8135/97/$17.00 © 1997 Elsevier Science Ireland Ltd. All rights reserved.

PII S 1053-8135(96)002 1 3-2

1. Introduction

Post-polio syndrome (PPS) is the term most commonly used to describe the new difficulties which may occur many years after recovery from paralytic poliomyelitis [1-7]. Although many symptoms may be reported by these patients, the most commonly reported are new weakness, fatigue, and pain. Therefore, these three symptoms have been used to define PPS. This article will concentrate on the symptoms of new

weakness and fatigue, because these symptoms are most likely referable to the motor unit. Currently, it is unclear how the symptom of pain, which is uncommmon in the classical motor unit diseases such as amyotrophic lateral sclerosis, is related to disease of the motor unit.

Although the definitive etiology of PPS (new weakness, fatigue) is unclear, a consensus as to the most likely cause is beginning to emerge. Jubelt and Cashman [4] reviewed nine possible causes of PPS. These included (1) chronic poliovirus infection, (2) death of remaining motor neurons with the normal ageing process, (3) premature ageing of cells permanently damaged by poliovirus, (4) premature ageing of remaining normal motor neurons due to an increased metabolic demand, (5) loss of muscle fibers in enlarged, reinnervated motor units with age, (6) predisposition to motor neuron degeneration because of glial, vascular, and lymphatic damage caused by poliovirus, (7) poliomyelitis-induced vulnerability of motor neurons to secondary insults, (8) genetic predisposition of motor neurons to both poliomyelitis and premature degeneration, and (9) an immune-mediated mechanism. The most likely possiblity, that of a peripheral disintegration of enlarged post-polio motor units, which was first proposed by Wiechers and Hubbell [8], will be discussed in greatest detail.

The normal ageing process which is associated with a gradual dropout of motor units [4,9-11] and other changes such as growth hormone and insulin-like growth factor-1 (IGF-1) deficiency [12-16] is most likely a contributing factor. Overuse [17,18] and conversely disuse [19] are other probable contributing factors for the development of PPS. Still uncertain is the significance of poliovirus genome fragments detected in cerebrospinal fluid of PPS patients [20-27], and the role of immune mechanisms [3,28-31].

2. Peripheral disintegration of enlarged post-polio motor units and new weakness in PPS

Acute paralytic polio involves motor neuron invasion by poliovirus, and is primarily a disease of the motor unit (defined as a motor neuron together with all the muscle fibers that it innervates). Pathological studies have revealed that poliovirus can also produce lesions in the cerebral cortex, primarily in the precentral gyrus, hypothalamus, thalamus, motor nuclei of the brainstem, reticular formation, vestibular nuclei, roof nuclei of the cerebellum and neurons in the intermediate columns [32,33]. During acute polio, motor neuron invasion can result either in cell death or injury as shown in Fig. 1 [4,32]. Motor neuron death will cause denervation of the muscle fibers it supplies, which may produce clinical weakness. Pathological studies have revealed that in limbs with minimal paralysis or normal function, up to 20% of the motor neurons could be destroyed [34]. During the recovery process following acute polio, remaining brainstem and spinal cord motor neurons can elaborate new branches, or axonal sprouts. Sprouts can form from three areas of a motor neuron; from the terminal axon, from the proximal unmyelinated axon, or from the more proximal nodes of Ranvier. These sprouts can reinnervate muscle fibers which have lost their innervation due to acute polio (Fig. 1). Sprouting can restore the capacity of voluntary muscle fiber contraction, and thus improve clinical strength. In addition to sprouting, muscle fiber hypertrophy of innervated muscle can contribute to the recovery of strength after paralytic polio.

Fig. 1. Normal: Three normal motor units are illustrated. Acute Polio:

Poliovirus invasion of one motor neuron produces degeneration of the motor

neuron with denervation of muscle fibers innervated by that neuron.

Recovery: Recovery following paralytic polio occurs by local sprouting from

surviving motor neurons with reinnervation of some or all muscle fibers.

Recovery may also involve muscle fiber hypertrophy (not illustrated). Post

polio syndrome: A distal degeneration of enlarged post-polio motor units with

denervation of muscle fibers is believed to be the most likely cause of post

polio syndrome.

This figure is reprinted with permission from Milestone Medical

Communications, A Division of Ruder-Finn, from a disease management

monograph entitled ‘Current Trends in Post-Poliomyelitis Syndrome’ (1996).

Motor neuron sprouting produces at least two changes in a motor unit. First, sprouting increases motor unit size. Muscle biopsy studies have shown that after recovery from acute paralytic polio, motor neurons may be innervating up to eight times the number of muscle fibers they would normally supply [35]. Other studies have shown that even with a loss of 50% of motor neurons supplying a particular muscle, sprouting can achieve complete reinnervation with normal muscle strength [36]. Second, motor neuron sprouting can produce fiber type grouping. There are at least three histochemical muscle fiber types, which in a normal muscle are distributed in a ‘mosaic’ pattern throughout a muscle fascicle. The histochemical type of a muscle fiber is determined by the motor neuron by which it is innervated. Thus, local motor neuron sprouting will produce a grouping of histochemically similar muscle fiber types.

Wiechers and Hubbell [8,37] have proposed that these abnormally enlarged motor units after acute paralytic polio are not indefinitely stable, but that terminal axonal sprouts degenerate over time producing denervation of muscle fibers (Fig. 1). It is possible that some of these denervated muscle fibers may become reinnervated by sprouts from neighboring motor neurons, producing a continuous ‘remodeling’ process of the post-polio motor units. However, some of these muscle fibers will become permanently denervated, producing a gradual denervation with increasing weakness. The investigators also demonstrated that jitter on single fiber electromyography (SFEMG; a measure of neuromuscular junction function and thus terminal axonal integrity in polio muscles) increased with time since acute polio. Even though no other investigators have been able to reproduce these results, the theory based on these findings has been upheld by other studies.

Muscle biopsy studies probably provide the best evidence for the Wiechers and Hubbell hypothesis. A muscle fiber that has lost its innervation for a few weeks’ time can display fiber atrophy and is termed an angular atrophic fiber on muscle biopsy. If the fiber remains denervated for months, it becomes a tiny ‘nuclear bag.’ Post-polio muscles on biopsy contain isolated angular atrophic fibers which were most likely denervated a few weeks prior to the biopsy. In addition, many extremely atrophic nuclear bags are found, some of which may be present from the original illness. The finding of isolated atrophic fibers suggests degeneration of terminal axons, as hypothesized by Wiechers and Hubbell. If PPS were a motor neuron disease (such as amyotrophic lateral sclerosis), then it would be expected that the muscle fibers of entire motor units would become simultaneously denervated. Even though some group atrophy is found on post-polio muscle biopsies, the predominant finding is scattered fiber atrophy. Because of these findings, new weakness in PPS is most likely due to degeneration of terminal axons, and not to death of motor neurons.

Despite the above findings, there are some difficulties with this hypothesis. Evidence for denervation (both on muscle biopsy and electromyography studies), occurs both in patients with past polio who are

noting new weakness, and in patients with past polio without new weakness [38]. In addition, a specialized electrophysiologic technique, macro-electromyography (macro-EMG; which can estimate motor unit size) does not reproducibly detect a gradual decline in motor unit size. In one study [39], macro motor unit potential amplitudes were found to be smaller in post-polio muscles with new weakness and atrophy than in post-polio muscles of normal strength or in weak but stable post-polio muscles. This would be consistent with the Wiechers-Hubbell hypothesis. In another study where macro-EMG was performed prospectively on subjects, motor unit size actually appeared to increase over time after acute polio [40].

3. Neuromuscular junction defects and muscle fatiguability in PPS

Fatigue in PPS is probably the major and most disabling symptom in PPS [2,41]. It can be either general or muscular, but frequently both occur concurrently. General fatigue is usually described as a ‘flu-like’ exhaustion, and is typically worse with physical activity and later in the day. Manifestations can include an increased sleep requirement, naps during the day, and decreased concentration. Muscle fatigue (or muscle fatiguability) is defined as increased muscle weakness with exertion, which improves with rest. However, when PPS patients have been compared to controls, the symptom of general fatigue occurred with a similar frequency in both groups, but muscle fatigue occurred significantly more commonly in PPS [42]. Therefore, muscle fatigue appears to be a unique and characteristic feature of PPS.

General and muscular fatigue in PPS have been attributed to a number of possible central and peripheral causes [43]. Proposed etiologies of central fatigue include chronic pain, respiratory dysfunction, ‘type A’ behavior, sleep disorders, dysfunction of the reticular activating system, and reduced dopamine secretion [44-48]. Possible causes of peripheral fatigue that involve the motor unit include metabolic exhaustion of

massively enlarged post-polio motor units, neuromuscular junction transmission defects, overuse myopathy, and fiber type disproportion [4,18,49-51].

Because of similar clinical and electrophysiological features of PPS with myasthenia gravis (a known disorder of the neuromuscular junction), we have hypothesized that muscle fatigue in PPS can be attributed to neuromuscular junction transmission defects. Muscle fatigue observed in PPS is reminiscent of that in myasthenia gravis. In addition, both disorders have evidence for neuromuscular junction defects on SFEMG studies as well as on repetitive stimulation studies [3,8,38,52-54].

If terminal axonal degeneration is the cause of new weakness in PPS, it is likely that there is a period of terminal axonal dysfunction that may preceed degeneration by months to years. This period of terminal axonal dysfunction may be amenable to potential therapies that would not be useful once degeneration and denervation has occurred. Terminal axonal dysfunction may manifest itself as ineffective acetylcholine release at the nerve terminal. Terminal nerve fibers release acetylcholine into the neuromuscular junction, which then binds to acetylcholine receptors on muscle cells. This can then produce a muscle contraction. Normally, acetylcholine is rapidly broken down in the neuromuscular junction by the enzyme acetylcholinesterase. Many investigators have reported evidence for neuromuscular junction transmission defects in patients with past paralytic polio. These have included increased jitter on SFEMG, a decrement on repetitive stimulation, and an increased sensitivity to nondepolarizing muscle relaxants [3,8,38,52,56].

Investigators who have found increased jitter on SFEMG have intrepreted this finding as evidence for ongoing denervation and reinnervation in post-polio motor units as well as defective neuromuscular juction transmission. This notion was supported by findings in a recent stimulation SFEMG study which evaluated jitter at varying stimulation frequencies [57]. In a large proportion of PPS patients, jitter was significantly higher at high stimulation frequencies than at low stimulation frequencies. The patients who displayed this phenomenon were a significantly longer time since acute polio, indicating that this may be

an acquired defect following paralytic polio. In contrast, this phenomenon was a rare finding in normal controls. In addition, neuromuscular junction defects in PPS can be ameliorated with the anticholinesterase edrophonium [51], providing further evidence for defective acetylcholine release as a cause for neuromuscular junction transmission defects in PPS.

Repetitive stimulation studies have also provided evidence for neuromuscular junction defects in patients with previous polio. Hodes [52] found a decrement of the compound muscle action potential amplitude on repetitive stimulation in patients with previous paralytic polio. He also reported an amelioration in this abnormality with anticholinesterase agents. More recent studies have shown that the decrement of the compound muscle action potential amplitude is apparent at high stimulation frequencies, but not low stimulation frequencies in patients with PPS [58]. This finding is consistent with previous SFEMG studies, and also suggests that acetylcholine release may be a limiting factor.

Post-polio patients are also known to have an increased sensitivity to non-depolarizing relaxants such as D-tubocurarine, pancuronium, and gallamine [56]. This suggests that acetylcholine release may be suboptimal in motor units following paralytic polio.

Muscle biopsy studies provide further evidence for neuromuscular junction transmission defects in post polio muscles. Electron microscopy studies of post-polio neuromuscular junctions show dilated or bizarre terminal axons with reduced acetylcholine vesicles [59]. In addition, muscle of patients with past polio has been studied histochemically with neural-cell adhesion molecule (N-CAM). In normal adult muscle, N-CAM is found only at end plates, satellite cells, and intramuscular nerves [60]. Surface and intracellular N-CAM is known to accumulate in experimental denervation, paralysis, or fiber regeneration [55,61]. N-CAM immunoreactivity occurs within two days of transection, which is long before conventional muscle biopsy criteria of denervation. N-CAM then disappears on reinnervation or complete regeneration [55,61]. In addition, NCAM immunoreactivity on myofibers has been found to be absent in normal muscle, but present in patients with ongoing denervation or myopathies with prominent fiber degeneration and regeneration [55]. In patients with past paralytic polio (both stable and those with new weakness), N-CAM expression in non-atrophic muscle fibers can be 10% or more [38]. Because less than 1% of muscle fibers in muscle of patients with past paralytic polio are permanently denervated [38], many post-polio muscle fibers may have borderline transmission of nerve impulses. Thus, N-CAM studies in post-polio muscle are consistent with significant and widespread neuromuscular junction transmission defects.

4. Contributing factors to post-poliomyelitis syndrome

Contributing factors to the development of PPS can be the normal ageing process, overuse, and disuse. The normal ageing process is known to involve a gradual dropout of motor neurons, and a decline in growth hormone and consequently IGF-1. Normal loss of motor neurons becomes prominent after age 60, and the superimposition of this process on the already limited number of motor neurons present after paralytic polio may contribute to the development of PPS [4,9-11]. Plasma IGF-1 has been reported to be low in patients with prior paralytic polio (including those with PPS) as compared with healthy controls [15,16], although another study did not report this finding [62]. Despite these contradictory findings, the normal decline of growth hormone and IGF-1 could contribute to PPS. Growth hormone stimulates IGF-1 production. Both growth hormone and IGF-1 support regeneration of peripheral nerves after nerve injury, including sprouting, and muscle fiber hypertrophy [63-68]. In addition, in one analytic epidemiologic study a greater age at presentation to clinic was a risk factor for PPS [69], whereas another study [70] did not confirm this finding.

Overuse is also thought to be a contributing factor to PPS. Knowlton and Bennett [17,71] reported several

cases of individuals 2-23 years following paralytic polio, and concluded that overuse produced increased weakness. Perry and co-workers [18] performed dynamic EMG studies during gait in 34 PPS patients, and found evidence of overuse primarily in the biceps femoris and quadriceps muscles. The investigators concluded from these and other studies [72] that overuse was the cause of PPS. In addition, increased creatinine kinase (CK) levels have been found in symptomatic patients after polio, but not in equally weak asymptomatic patients after polio [70]. CK levels were found to be significantly correlated with distance of ambulation in postpolio patients, suggesting that exercise is the cause of elevated CK in this population [73]. Since elevated CK levels can be a marker for muscle injury, the increased CK levels may indicate muscle injury or overuse in post-polio patients. In our case-control study, we found that a greater length of time after paralytic polio was a risk factor for PPS, and that muscle pain (especially that associated with exercise), joint pain, and a recent weight gain were associated with PPS [69]. All of these factors can be markers of overuse, providing further evidence for this theory.

Muscle disuse can also be a contributing factor to the onset of PPS. Disuse is well known to produce muscle weakness and deconditioning in normal individuals [74], and most likely produces similar changes in patients with past paralytic polio [19]. Patients with past polio have been noted to have short term increased weakness after a period of decreased activity secondary to illness or injury [75]. In our clinical experience, we have noted that periods of decreased activity may precipitate the onset of increased weakness.

5. Diagnosis of post-polio syndrome

The diagnosis of PPS is one of exclusion, and is clinically based. There is no specific diagnostic test which can distinguish symptomatic from asymptomatic survivors of past paralytic polio [38]. Conventional EMG, SFEMG, muscle biopsy, and N-CAM immunohistochemical studies in patients with PPS and in asymptomatic polio survivors are consistent with ongoing denervation in both groups of patients [38]. In addition, abnormalities indicating active denervation were found with similar frequency in both patient groups.

There are no well established diagnostic criteria for PPS. Mulder and coworkers [76] first proposed criteria for the onset of new weakness many years after acute paralytic polio: (1) a credible history of acute paralytic polio, (2) partial recovery of function, (3) a period of stability of at least 10 years’ duration, and (4) the later development of progressive new weakness. They also suggested that there should be no other cause of the new weakness. In more recent years, Halstead [47], has proposed more complete criteria for PPS. They include: (1) previous acute paralytic polio which is confirmed by history, physical examination, and EMG studies, (2) a period of recovery followed by a period of neurological and functional stability of at least 20 years’ duration before the onset of new difficulties, (3) the gradual or abrupt onset of new neurogenic weakness which may or may not be accompanied by other difficulties such as excessive fatigue, muscle pain, joint pain, decreased endurance, decreased function, and atrophy, and (4) the exclusion of medical, orthopedic, or neurologic disorders which could be producing the new problems. According to this definition, new weakness should not be due to disuse although this may be difficult to ascertain. In our opinion, a more practical definition of PPS would include the above criteria with the exception of EMG studies which should be reserved for those with unclear evidence for past paralytic polio based on history or physical examination, and those who may have certain superimposed neurologic conditions (such as compressive neuropathies, or peripheral neuropathies).

6. Differential diagnosis of post-poliomyelitis syndrome

In a patient with past paralytic polio presenting with new symptoms, the diffential diagnosis will be

dependent upon the specific symptoms of the patient. It is also important to note that many patients with past paralytic polio have developed a distrust or dislike of the medical profession (perhaps due to many months of hospitalization at a young age), and may come to clinic without seeing a physician for decades. In this situation, it is important to develop a trustful relationship with the patient and to consider other disorders which could be producing any new symptoms, and which may have nothing to do with previous paralytic polio. For example, hypothyroidism and rheumatoid arthritis may produce pain, weakness, and fatigue. In our experience, undiagnosed or undertreated hypothyroidism occurs fairly frequently in patients presenting with new symptoms to a post-polio clinic, and adequate treatment results in complete or partial resolution of ‘PPS.’

General fatigue is a very common symptom in the general population, and may be due to a variety of causes. Some of these causes can include respiratory dysfunction, sleep apnea, depression, sleep abnormalities, chronic pain, and a variety of medical disorders including hematologic abnormalities (e.g. anemia), endocrinological abnormalities (e.g. hypothyroidism), cardiac dysfunction, cancer, chronic systemic infections, and rheumatological disorders.

Pain in patients with past paralytic polio can be due to a variety of causes. It can be caused by muscular abnormalities, joint and soft tissues abnormalities, and other superimposed neurological abnormalities. Possible causes for muscular pain include a ‘post-polio muscular pain’ [19], muscular overuse, muscular cramps, fasciculations, and fibromyalgia [77]. We have found that fibromyalgia occurs frequently in a post-polio clinic. Wolfe et al. showed that 10.5% of patients met the criteria for fibromyalgia [78], whereas another 10.5% had a fibromyalgia-like syndrome with 5-10 tender points on examination. Patients with past polio who had fibromyalgia responded to specific treatment for this condition [77]. Treatments included low-dose, night-time amitriptyline, night-time cyclobenzaprine, fluoxetine, naproxen, and aerobic exercise [77]. Some of the symptoms of fibromyalgia (especially pain and fatigue) were very similar to those of PPS, however the two disorders also occurred concurrently [77]. Joint and soft tissue abnormalities which may produce pain include osteoarthritis, tendonitis, bursitis, degenerative disc disease, scoliosis, ligamentous strain, joint deformities, and failing joint fusions. These conditions in many cases most likely result from chronic overuse or abnormal use of joints and extremities due to muscle weakness as a result of past paralytic polio and PPS. Some superimposed neurological abnomalities which can produce pain include peripheral neuropathies, radiculopathies, and spinal stenosis.

New weakness can be due to other superimposed neurological disorders, however a variety of medical problems can also produce the symptom of new weakness. Some neurologic diseases to be considered when evaluating a patient with past paralytic polio and complaints of new weakness are listed in Table 1. These include disorders which are relatively common in the adult population such as spinal stenosis, radiculopathy, and cervical spondylosis. Other motor neuron diseases such as amyotrophic lateral sclerosis can also occur, however the frequency of this disease is not increased in those who have recovered from paralytic polio.

Table 1 Neurological disorders to exclude in diagnosing PPSa

 

 

Adult spinal musuclar atrophy

Amyotrophic lateral sclerosis

Cauda equina syndrome

Cervical spondylosis

Chronic inflammatory demyelinating polyneuropathy

Diabetic amyotrophy

Entrapment neuropathy

Heavy metal toxicity

Inflammatory myopathy

Multifocal motor conduction block

Multiple sclerosis

Myasthenia gravis

Parkinson’s disease

Peripheral neuropathy

Radiculopathy

Spinal cord tumor

Spinal stenosis

aThese diseases may also occur concurrently with PPS. This table is reprinted with permission from Milestone Medical Communications, a Division of Ruder Finn, from a disease management monograph entitled ‘Current Trends in PostPoliomyelitis Syndrome’ (1996).

 

 

7. Conclusion

In conclusion, it may be useful to consider PPS as being caused by two abnormalities in the motor unit. The first is a progressive lesion which is degeneration of terminal axons which results in permanent slowly progressive new weakness. The second is a fluctuating lesion most likely secondary to defective synthesis, storage, and release of acetylcholine, which results in neuromuscular junction transmission defects and in the symptoms of muscle fatiguability and secondary generalized fatigue. Other factors which may contribute to the development of PPS are ageing, overuse, and disuse. The diagnosis of PPS involves the exclusion of other conditions which could produce similar symptoms in a patient who presents with symptoms and signs typical for PPS.

Acknowledgements

This work was supported in part by the Fonds de la recherche en santé dy Québec, and the Association Polio Québec.

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