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Post-Polio Health (ISSN 1066-5331)

Vol. 7, No. 2, Spring 1991

A Ten Year Experience

Stanley K. Yarnell, MD, Saint Mary's Hospital Post-Polio Clinic, San Francisco, CA

The following paper was prepared for Post-Polio Conference III – Perspectives for the Nineties held February 1-2, 1991, at the Oakland Hyatt Regency in Oakland, CA, USA.

The Original Effects of the Poliovirus

To more easily understand the late effects of polio, it is important to understand the original effects of the poliomyelitis virus. The portal of entry for the poliovirus was oral, and the infection in its first stage was in the gut cells lining the intestine. Many people infected with the virus at this stage thought they simpily had gastrointestinal flu with symptoms of diarrhea and nausea. For a significant percentage of the people infected, the disease ended at this point.

But for some, the virus continued to multiply and spilled over into the blood stream, signaling the viremia stage of the infection. Symptoms then were not unlike a more generalized influenza, with fever, chills, malaise and achiness. Once again, for a significant percentage of patients, the disease process ended there. However, in a small percentage of the patients, the virus crossed over into the central nervous system and infected the anterior horn cells. These individuals contracted "paralytic" polio.

The distribution of weakness or paralysis depended on which anterior horn cells were involved. Spinal anterior horn cell involvement resulted in weakness or paralysis in the arms, legs and trunk to one degree or another. Bulbar (brainstem) anterior horn cell involvement resulted in visual, swallowing or breathing difficulties in any combination.

It is this period of fever, weakness, paralysis and muscle pain that many polio survivors (or their parents) remember. This was the time when infected motor neurons were dying, leaving all the muscle fibers they innervated orphaned (or denervated). If all the motor neurons that supplied a particular muscle died, the result was complete paralysis of that muscle. If only a percentage of the motor neurons died, the muscle was only weakened, but not completely paralyzed.

Many polio survivors remember having muscles completely paralyzed that started to move again, although weakly, after a period of a few weeks. That occurred because some of the anterior horn cells were simply shocked when neighboring anterior horn cells died. These nonfunctioning anterior horn cells were not dead but stunned by the swelling caused by adjacent nerve cell destruction. As days and weeks passed, the swelling subsided and the surviving anterior horn cells revived. Kenny hot packs and stretching helped control the pain and contracture of the denervated muscle. With time and exercise, the muscle got stronger.

Over the course of months and years, many polio survivors got stronger in a previously weakened or paralyzed muscle and were able to discard braces or wheelchairs. This was not only because of hard work and exercise but also because of a phenomenon called sprouting. Denervated or orphaned muscle fibers within the same muscle sent out a chemical distress signal that caused tiny sprouts to grow from the terminal nerve branches of neighboring, surviving motor neurons. Very slowly these sprouts grew over to the orphaned muscle fibers and reinnervated them, causing the motor unit to grow in size. In fact some motor units sprouted to innervate three to four times as many muscle fibers as Mother Nature had originally intended. As a result, polio survivors felt stronger, and this pattern of strength and weakness remained stable for the next 20 to 30 years.

The Late Effects of Polio

Since 1981, 483 post-polio patients have been seen at St. Mary's Hospital Post-Polio Clinic. When the data collected by Barbara L. Bammann, MD, at Alta Bates-Herrick Rehabilitation Hospital and by Michael Berlly, MD, at Santa Clara Valley Medical Center are added, there is a wealth of statistics and information. In all, 711 patients have been examined in the Bay Area Post-Polio Clinics. The ages range between 30 and 76. The following material is based in large part on these statistics.

FATIGUE: The most frequent symptom as unaccustomed fatigue (79%). During the past decade, a number of investigators have looked at the problem using a variety of research tools, including muscle biopsies, electromyography, single fiber electromyography, immunologic and metabolic blood studies, biomechanical and gait analysis, and psychometric testing. The picture that has emerged from this data suggests that after 30 years, the metabolically overburdened surviving motor neurons appear to have become incapable of supporting the integrity of all the distal nerve terminals, resulting in defective neuromuscular transmission.

To better understand this, visualize what happens at the junction of the nerve and muscle under the usual circumstances. The electrical impulse travels from the anterior horn cell, down the nerve fiber to the tiny terminal nerve endings, which contact the individual muscle fibers. The arrival of the electrical impulse at the terminal nerve ending causes the release of a chemical (acetylcholine), which in turn causes the electrical impulse to penetrate into the muscle fiber, resulting in contraction of that tiny muscle fiber. In polio survivors, repeated discharges of the large reinnervated motor unit results in a failure of some of the muscle fibers to fire, thereby not contributing to the force of contraction. Polio survivors experience this as fatigue or a loss of stamina.

Interestingly, all polio survivors have defective neuromuscular transmission, but not all survivors complain of decreased stamina, so clearly other factors must be playing a role. The number of surviving motor units is probably an important factor, as well as the force generated during a particular task. Improper pacing during day-to-day activities and deconditioning following illness, surgery or trauma are also factors to be considered. Finally, some polio survivors complain of sleepiness as well as decreased stamina. and this "mental fatigue" may result from the stress of chronic pain or the stress of dealing with secondary disability.

WEAKNESS: 410 (58%) of the polio survivors examined in the Bay Area's Post-Polio Clinics were found to have new or increasing weakness. This was based on the patient's history including his or her functional abilities, the physical examination, and appropriate laboratory studies, including electromyography (EMG), x-rays and CT scans, Magnet Resonance Imaging (MRI), metabolic or electrolyte studies, and pulmonary function testing with blood gases. Usually, we were unable to track down old manual muscle testing records, but they were used when available.

A significant number of the patients had new or increasing weakness for reasons not directly related to their polio residuals. Radiculopathy (pinched nerve root) accounted for 40 patients (10%) of the total with new weakness. Compression neuropathy (pinched peripheral nerve, as in carpal tunnel syndrome) accounted for 31 patients (8%) of the cases of progressive weakness. A few other cases were not at all related to old polio residuals and included three individuals who developed multiple sclerosis, three with peripheral neuropathy, one with brachial plexitis, and one with lithium toxicity. All of these cases underscore the importance of careful examination in order to rule out other treatable causes of weakness. Not every ill can be blamed on the late effects of polio!

Having stated that, we note that there were a large number of patients who did have increasing weakness which was directly attributable to the late effects of polio. 114 patients (28%) of the total with new weakness had acute overwork weakness, while 211 (48%) were diagnosed with post-polio muscular atrophy (PPMA). Some clinicians would argue that acute overwork weakness and post-polio muscular atrophy are one and the same. We have chosen to separate them for record keeping purposes and for prognostic reasons.

The idea of overwork weakness is not a new one. Dr. Bennett, the former medical director of Georgia Warm Springs, described it clinically in 1958, and there are other less well-articulated references in the medical literature to worsening weakness in polio survivors going back nearly 100 years. Clinically, polio survivors who have engaged in excessively strenuous activities like tennis, weight lifting, stair climbing, etc., have noted the sudden onset of weakness in particular muscle groups overused in that particular activity. The muscle may lose more than a full grade of strength on the manual muscle test. Even though it may take months and with proper rest, the strength may return nearly to the level it was prior to the strenuous activity. This reversible weakness is what we refer to as acute overwork weakness.

Cumulative research suggest that the old overburdened motor neuron, which has been driving many more muscle fibers than it was meant to drive is so metabolically exhausted by the strenuous activity that some of the terminal nerve endings die back, leaving many of the muscle fibers of the same motor unit orphaned again. If the weakened muscle group is allowed to rest (by stopping the offending activity or bracing, for example), new sprouts will grow and recapture the lost muscle fibers. The number of surviving motor units in a particular muscle, the pattern of muscle substituion, and the force generated by that muscle are crucial variables.

Chronic overwork weakness, or what has been called post-polio muscular atrophy (PPMA), differs inasmuch as there is no singular event of strenuous activity or exercise that signals the onset of increasing weakness. Rather there is a very slow and gradual loss of strength with accompanying atrophy of a particular muscle group. And no amount of rest will reverse the weakness. It appears, once again, that the overburdened motor unit is the common problem. The variables appear to be the intensity of work imposed on a particular muscle group by the function required of it over a long period of time. The overburdened motor neuron is unable to send out new sprouts to capture the orphaned muscle fibers, which have become denervated slowly from "pushing" in order to complete ordinary day-to-day activities.

RESPIRATORY PROBLEMS: Of the total number of patients seen in the Bay Area's Post-Polio Clinics, only 115 (16%) were classified as having worsening respiratory problems. This included people who required increased mechanical assistance like intermittent positive-pressure ventilation (IPPV) during the day, more effective mechanical assistance necessitating a change in type of ventilator, and those who began using positive pressure by mouth ventilation at night. There were other respiratory problems, but these were not included in the statistics. Recurrent bronchitis was a frequent enough problem to warrant mentioning, even though the patients for whom it was a problem had a perfectly adequate cough and no difficulty handling secretions. Except for two patients, there were no immune abnormalities. The problem seems to be more of a chemical bronchitis (as opposed to infection) caused by night-time aspiration of tiny amounts of stomach acid, which refluxes from the stomach into the esophagus because of hiatus hernia. Fully 167 polio survivors (23%) have symptomatic indigestion secondary to hiatus hernia. The figure may be so large in polio survivors because of the high percentage of scoliosis, which is usually associated with chest wall rotation. There are other effects of scoliosis on breathing, especially people who have any residual weakness of the deep breathing or coughing muscles. Despite reports of sleep apnea in polio survivors, we have seen only one documented case.

JOINT AND MUSCLE PAIN: Various musculoskeletal aches and pains were a problem for 559 polio survivors (74%). Many people had more than one site of pain and had been bothered by one pain or another for many years. As you can see from the statistics that follow, most polio survivors suffer from chronic pain, which for some can be quite disabling. Our statistics break down the different sources of pain.

Nearly all polio survivors (99% of our patients) had scoliosis. Scoliosis per se does not hurt, but the long standing effects of rotation and curvature of the spine have been associated with conditions that do hurt. We found that 178 people (34%) had facet arthropathy or wear and tear arthritis of the little joints of the spine. 216 (41%) had degenerative disc disease, sometimes in combination with facet arthropathy. 67 (12%) had pain in the back and legs or in the neck and arms due to radiculopathy (pinched nerve root). 59 patients (11%) had lumbar spinal stenosis, all of whom were over the age of 60. 23 (4%) had a problem with sacroiliac joint pain. All but one of these people were long-time wheelchair users with pelvic obliquity associated with scoliosis. Three patients had piriformis syndrome.

The other joints in addition to the ones of the spine showed signs of wear and tear arthritis. As in the case of the back, abnormal biomechanics and overuse (or sometimes abuse) caused wear and tear of degenerative arthritis. The shoulder was affected in 116 people (22%), while the knee was affected in 111 (21%). Degenerative arthritis was present in the hip in 58 (11%), in the ankle/foot in 31 (6%), and in the wrist in 21 (4%). Interestingly, if a leg was braced because of the weakness, the arthritis generally developed on the unbraced side, which had been the side of major weight bearing for many years.

In addition to joint pain, there were a number of soft tissue sources of pain. Bursitis/tendonitis was generally associated with underlying arthritic changes and was present in 171 patients (32%). Carpal tunnel syndrome was present in 117 polio survivors (22%) and was usually associated with crutch or cane walking or pushing a wheelchair. Fibrositis or myofascial pain syndrome, usually associated with underlying degenerative changes in the spine, was present in 68 patients (13%). 59 patients (11%) complained of muscle tension headaches, which was associated with degenerative cervical changes. 15 (3%) patients complained of burning and tingling in the hand and arm due to ulnar compression neuropathy from leaning their elbows on the wheelchair armrests. Other compressional neuropathies causing pain and discomfort included tarsal tunnel syndrome (not unlike carpal tunnel syndrome, but in the foot) and lateral femoral cutaneous neuropathy. Finally, there were 11 cases of thoracic outlet syndrome, associated with chronic slumped shoulders. We did not collect statistics on fractures.

COLD INTOLERANCE: Forty-one percent of the polio survivors complained of worsening cold intolerance. For nearly everyone it was not a new problem, but one that had been present since the onset of polio to a less bothersome degree. There seem to be two manifestations of the problem. One we have dubbed the "purple foot syndrome," which is characterized by painful coldness in one or more limbs, usually in the limb most affected by residual atrophy. Spouses also complain of this problem, especially in the middle of the night! It appears that some of the sympathetic nerve fibers were affected originally, and these fibers are the ones that constrict the blood vessels of the skin in response to cold. Normally, when we are exposed to cold, the blood vessel of the skin constrict to shunt blood away from the surface of the skin down to the underlying bone and muscle where heat can be conserved and the core body temperature maintained at 98.6 degrees. Some polio survivors have lost that ability to shunt blood away from the skin, and so heat radiates away from the affected limb and it cools down. The best treatment is an elastic stocking and good woolly socks, foot warmers at the bottom of the bed, and an insensate spouse!

The other part of the problem is decreased muscular performance in the presence of cold. Many polio survivors find they are unable to swim in an unheated pool, or they find that they have more trouble walking in cold winter weather. This is explained by the fact that when muscle is cooled, defective neuromuscular transmission is made worse. If you suffer from cold intolerance, you can only be advised to try to avoid cold exposure and "button up your overcoat."


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