Post-Polio Health (ISSN 1066-5331)
Vol. 6, No. 3, Summer 1990
Prescription for Weakness, continued
DR. DARIA TROJAN: New or increased weakness is a major symptom in individuals with post-polio syndrome. Clinically, this weakness is manifested as either a permanent new loss of muscle strength or waxing and waning strength which is related to activity. The latter condition is known as muscle fatigability and is defined as increased weakness on exertion improving with rest.
Currently, the diagnosis of new weakness and muscle fatigability in individuals with previous polio remains clinical. There's no known diagnostic test which can discriminate symptomatic from asyrnptomatic post-polio survivors.
In an earlier study by our group, (NEJM 1987;317:712), it was concluded that abnormalities seen on electromyography (EMG), single-fiber electromyography and muscle biopsy occurred with equal frequency in both symptomatic and asymptomatic individuals. Both groups showed evidence of ongoing or active denervation. (Denervation is loss of nerve supply to the muscle.) However, more recent data obtained from macro-EMG studies suggests that the cumulative loss of muscle fibers is greater in symptomatic than asymptomatic patients. Macro-EMG is a special type of EMG test which can measure motor unit sizes, or the number of muscle cells a nerve cell supplies.
Survivors with prior polio show evidence of neuromuscular junction communication defects on a special EMG test called single fiber EMG. (The neuromuscular junction is the point where the nerve cell communicates with a muscle cell and causes a muscle contraction.) Similar neuromuscular junction communication defects are seen in other neurological disorders. These defects may be the cause of muscle fatigability which is observed in post-polio survivors and in individuals with other neurological disorders.
Treatment of new weakness and muscle fatigability can take many forms.
First, treatment of any associated medical conditions must be instituted. Some medical conditions may be a cause of weakness and fatigue, and they should be identified and treated. This is especially important for respiratory dysfunction.
Second, treatment of weakness and joint instabilities can include weight loss, physical therapy, orthotics (braces), mobility aids and orthopedic constructive procedures. Weight loss, when indicated, can reduce fatigue and reduce the amount of mechanical stress which is applied to already unstable joints. Physical therapy can include stretching exercises along with ambulation and mobility training. Orthotics, or braces, may also be necessary.
I would like to expand upon orthotic management of the more common bio-mechanical deficits. Foot drop during gait is caused by weakness of foot dorsiflexor muscles (muscles which bring the foot up) and is best managed by an ankle-foot orthosis. There are many varieties of ankle-foot orthoses including the cosmetic plastic and the traditional, double, metal upright ankle-foot orthosis.
Second is forward collapse while standing. This occurs secondary to weak leg extensor muscles (found on the posterior aspect of the leg). Usually when this is present only in one leg, no treatment is necessary. However, when both legs are affected, an ankle-foot orthosis can be used. In addition, a cane or crutch may be necessary.
A third problem is genu recurvatum or backward bending of the knee. This occurs because of weak quadriceps or knee muscles (found on the front of thigh) which causes the affected person to bend the knee back as much as possible to lock the knee and prevent knee collapse when standing on that leg. Over time, this can lead to severe backward bending of the knee due to stretching of muscles and ligaments. If not treated, this can cause pain and increased difficulty in walking. When the quadriceps muscle still has moderate strength, a knee brace can be used. In more severe cases, a long-leg brace or a knee-ankle-foot orthosis should be used.
A fourth problem which is common in post-polio survivors is genu valgum or lateral bending of the knee. This occurs secondary to weakness of hip abductor muscles or muscles which move the leg sideways, away from the body. Because of this weakness, a lateral-bending stress is placed on the knee which causes stretching of muscles and ligaments. This can also cause pain and increased difficulty in walking. This is best managed with a knee-ankle-foot orthosis.
The fifth problem is medio lateral (or side to side) ankle instability which occurs secondary to weak ankle and foot muscles. This can be treated with special foot orthotics or shoe inserts. In more severe cases, an ankle-foot orthosis may be necessary.
Other treatments of weakness and muscle fatigability for polio survivors are mobility aids, such as canes, crutches, and wheelchairs. Orthopedic reconstructive procedures may also be helpful.
General health measures, such as proper rest, nutrition and weight management should be instituted.
Frequent rest periods and naps throughout the day may be necessary to combat overwhelming fatigue which may actually produce more weakness.
Exercise can be useful. Aerobic exercise programs have been shown to produce improvement in energy efficiency and work capacity, while attenuated progressive resistive exercise programs have been shown to increase muscular strength in selected muscle groups. This type of exercise program involves progressive increases in the amount of weight lifted, however, a much lower starting weight is used than normally prescribed. Any exercise program should avoid fatigue as this may produce increased weakness. In general, low resistance, high repetition types of exercises are preferable.
Survivors may benefit from psychological support and counseling. Most individuals with the post-polio syndrome have had to overcome a severe disability earlier in life, and they may have difficulty coming to terms with a second disability.
Pyridostigmine, a longer acting medication, may be useful in the treatment of muscle fatigability. However, the more conventional treatments should be used first. Pyridostigmine can improve the communication between nerve and muscle cells at the neuromuscular junction and has been used to treat muscle fatigability and other neurological disorders. We are currently conducting a trial to assess the effect of pyridostigmine on fatigue and post-polio syndrome survivors.
In addition, we are studying the response of neuromuscular junction communication defects in the post-polio syndrome to edrophonium, a short acting medication which improves the communication between the nerve and muscle cells.
So far, 16 individuals have been treated with pyridostigmine. In ten, we assessed neuromuscular junctional communication by single fiber EMG before starting pyridostigmine. The single-fiber EMG measured jitter, an index of communication of the nerve cell with the muscle cell at the neuromuscular junction. (Specifically, jitter is defined as the variability between the time of firing of one muscle fiber and the time of firing of another muscle fiber when both are being triggered by the same nerve cell.)
Jitter is increased in post-polio survivors. We performed jitter measurements before and after edrophonium injection in ten post-polio survivors with muscle fatigability. Four patients were found to have a significant reduction or improvement in jitter with edrophonium, four patients had no change in jitter, and two patients experienced an increase in jitter with edrophonium.
To measure response of pyridostigmine to fatigue, several indices were computed for all 16 patients before and at least one month after starting treatment. The fatigue symptom scale as described by Hare and co-workers was used. Zero represents no fatigue while 4 represents unbearable fatigue. We also used a second fatigue scale developed by Dr. Neil Cashman. Zero refers to no fatigue or fatigue which does not interfere with activities of daily living. One refers to fatigue which interferes with activities of daily living. Two refers to fatigue which requires rest or sleep greater than 50% of the day.
We also used the modified Barthal ADL (activities of daily living) index which is used by many rehabilitation facilities to monitor effectiveness of treatment. The possible scores range from zero to 100, where zero refers to an individual who is entirely dependent on others for his activities of daily living and 100 refers to a person who is independent in activities of daily living. The mobility index which was used is modified from one developed by Klingaman and coworkers. Zero represents no ambulatory or walking difficulty, whereas a six refers to someone bedridden.
The results obtained for the 16 patients treated with pyridostigmine show that two individuals were unable to tolerate the medication; ten experienced a reduction in their fatigue which was seen as an improvement in fatigue indices; two showed improvement on ADL indices; one showed improvement in mobility index; and one was able to return to work after initiation of treatment. All four individuals who had a decrease or improvement of jitter with edrophonium on single fiber EMG testing also had a reduction in fatigue with the medication pyridostigmine. Four of the six with either no change in jitter or an increase in jitter with edrophonium and single fiber EMG experienced no change in fatigue with pyridostigmine. The remaining two with either unchanged jitter or increased jitter with edrophonium and single fiber EMG unable to tolerate the medication pyridosne. Thus edrophonium effect on jitter may predict response to an oral medication similar to edrophonium in the post-polio syndrome.
From these preliminary results we conclude that: 1) pyridostigmine may be an effective treatment of fatigue and muscle fatigability in selected individuals with the post-polio syndrome; and 2) response of fatigue to pyridostigmine may correlate with improvement of neuromuscular junction communication defects as seen by improvement on jitter on single fiber EMG testing with edrophonium. Further studies are in progress to substantiate these preliminary results.
In conclusion, treatment of weakness and muscle fatigability in the post-polio syndrome should consist of a multifaceted approach. It can include treatment of associated medical conditions, treatment of biomechanical deficits, general health measures, exercise, frequent rest periods, and psychological support. Treatment of muscle fatigability and fatigue may now also include pyridostigmine but only in certain monitored individual situations. However, if none of these treatments proves to be effective in certain situations, I have always been amazed at my patients' ability to treat themselves and make sure nothing comes in the way of certain things which they insisted on doing!