Abstract
During the first half of the 20th century, millions of people around the world, mostly children, acquired paralytic polio, also referred to as infantile paralysis. In 1955, polio vaccination started in the United States and shortly thereafter in other parts of the world. Over the past three decades, massive vaccination programs have been launched to completely eradicate polio, and in 2017 less than a hundred new cases were reported. Even though the global initiative to combat polio has been very successful, the long-term consequences of the initial infection will remain well into the 21st century. Many persons who recovered from the acute paralytic polio infection can several decades later experience new symptoms, such as muscle weakness, muscle fatigability, general fatigue, and pain during activities and at rest. This is referred to as postpolio myelitis syndrome (PPS) with several million people around the world being affected, making it one of the most common neuromuscular conditions. There is no treatment that can cure PPS or any medication that can delay its progression, but those who have PPS do benefit from taking part in an interdisciplinary comprehensive goal-oriented rehabilitation program. Such a program may reduce the consequences of the symptoms and the disability that these symptoms impose on their lives. Through rehabilitation, persons with PPS can acquire new skills, which, over time, contribute to a sense of control and an overall adaptation to a new but good life.
Definition
Poliomyelitis, also referred to as infantile paralysis, is a disease caused by an enterovirus that in about 95% of people only leads to minor flu-like symptoms. In less than 5%, the virus can affect the nervous system with a meningitis and high temperature, headache and stiff neck; this is referred to as nonparalytic polio. Yet, in about 1% of people, the polio virus leads to an acute motor neuron disease, so-called paralytic polio, with partial or total paralysis. In some people motor neurons in the brain stem are also affected, referred to as bulbar polio, causing breathing and swallowing problems.
During the first half of the 20th century, there were major polio epidemics throughout the world. Polio affected mainly children and countries in the Western world with good hygienic and sanitary standards. This occurred when other infectious diseases were being successfully prevented. At the end of the 1940s, several research discoveries led to a better understanding of poliovirus and opened up new opportunities for the manufacture of vaccine. The American organization the March of Dimes invested large sums of money, and the American researcher Jonas Salk started to develop a vaccine, which in 1954 was shown to be effective. General vaccination began in 1955 in the United States and shortly thereafter in other parts of the Western world. This rapidly led to a large reduction in the number of polio cases. In 1988, the World Health Organization decided to try to eradicate polio from the world. The campaign has been highly successful. Today, less than a hundred new cases are being reported annually. In 2017, there were only a few countries in Africa, Asia (mainly Pakistan and Afghanistan), and the Middle East (mainly Syria) where new cases are still reported. The original goal was that polio should be totally eliminated by 2000; however, this deadline has been postponed repeatedly.
It is well known that many polio survivors later in life develop new symptoms, referred to as poliomyelitis sequelae, late effects of polio, or just postpolio. Although sequelae of prior polio have been known since the end of the 19th century, it was not until the early 1980s that researchers came to agree on the term postpoliomyelitis syndrome (PPS) to describe the various symptoms that polio survivors may perceive. As there are no accurate statistics describing the number of people being affected by polio, we have no clear account of the number living with PPS. The figures in the literature vary, mostly depending on the definitions used, but it is generally agreed that around 60% of those who initially had paralytic polio will develop PPS. In the United States, it is estimated that more than 1 million survivors of polio live in the country; in the European Union (with a population of approximately 500 million inhabitants), the number is approximated to 600,000 polio survivors. With many young polio survivors in Africa and Asia, it is estimated that up to 10 million people around the world will need health care and rehabilitation during the next decades as a result of their poliomyelitis infection. This makes PPS one of the most common neuromuscular conditions and a challenge to rehabilitation professionals.
PPS is a neurologic disorder characterized by a collection of symptoms occurring decades after the initial paralytic polio. There are different definitions of PPS, but all are more or less based on the original description by Halstead and Rossi in 1985 and consist of five diagnostic criteria ( Table 147.1 ). At the March of Dimes international conference on PPS in 2000, diagnostic criteria were recommended, including a criterion that symptoms should persist for at least 1 year. Individuals with prior polio may perceive a number of new symptoms—the three most common are new muscle weakness, fatigue (muscle as well as generalized), and pain from muscles and joints at rest and during activities. Other, less frequently occurring, but equally disabling symptoms are respiratory problems, swallowing problems, and cold intolerance.
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The cause of PPS is not entirely clear, but it is generally agreed that the new symptoms (muscle weakness and fatigue) are due to a distal degeneration of axons in greatly enlarged motor units that developed during recovery after the acute paralytic polio. After the initial paralysis, motor units are enlarged as a compensatory mechanism. These enlarged motor units undergo a continuous remodeling, and at the age of around 50 years, people start to suffer from the “normal” age-related loss of motor neurons. This process of denervation and reinnervation could be accelerated in PPS owing to a premature dropout of motor neurons caused by neuronal damage from the initial infection, increased metabolic demand in the enlarged motor units, or overuse. The loss of whole, enlarged motor units without reinnervation would also contribute and lead to a progressive dropout of muscle fibers. Other reasons underlying PPS have been discussed during the past decades, such as persistent poliovirus infection; overuse weakness due to transition in contractile properties and firing frequency; weight gain; and combined effects of muscle overuse, disuse, and weight gain. On the basis of findings of raised concentrations of cytokines in the cerebrospinal fluid, an inflammatory process might also be present as part of PPS; even though there is evidence for systemic inflammation, the relationship with clinical deterioration remains tenuous. This has, nevertheless, led to the development of new treatment strategies that potentially could be beneficial for people with PPS (see the section on treatment).
Regardless of the underlying pathophysiologic mechanisms of PPS, it is a condition that is highly suitable for physicians in physical medicine and rehabilitation. There is no treatment that can cure PPS or any medication that can clearly delay its progression. However, those who have PPS can benefit from taking part in an interdisciplinary comprehensive goal-oriented rehabilitation program to reduce the consequences of the symptoms and the disability that these symptoms impose on their lives.
Symptoms
Muscle Weakness
Muscle weakness typically occurs in muscles involved during the acute infection but may also be experienced in muscles that were not clinically paralyzed originally. There is an association between the initial weakness and weakness occurring later in life. The greater the initial paralysis, the greater is the PPS-related weakness. Most people start to perceive the new weakness around the age of 50 years; however, the progression of strength losses is usually slow, with an approximate annual loss of 2% to 4%. Over 4 years, men seem to have a greater decline in muscle strength than women, indicating that gender could contribute to the progressive decline in muscle strength. A history of more rapid progression of muscle weakness during weeks or months could indicate an alternative diagnosis, such as myopathy (e.g., polymyositis) or motor neuron disorder (e.g., amyotrophic lateral sclerosis), and should require a thorough clinical investigation.
Fatigue
Fatigue in PPS can be either of muscle origin or more generalized. Muscle fatigue is commonly reported by people with PPS and is characterized by the inability to maintain muscle force. Muscle fatigue is linked to muscle weakness and muscle atrophy, and those with more pronounced muscle weakness also experience more muscle fatigue. Fatigue can also be described as more generalized and of central origin. This type of fatigue can be perceived as severe and persist for several years. It has been found to be associated with reduced physical functioning, increased body pain, reduced sleep quality, and psychological distress. Typically, this generalized fatigue is described as an influenza-like exhaustion that is often related to the amount of activities performed. Polio survivors usually feel fairly refreshed in the morning and become more fatigued as the day goes on. Some may even complain that they “hit a wall,” experiencing an almost paralyzing tiredness, and just have to lie down and rest, something that usually relieves the fatigue. It is not unusual for people who have had severe meningitis as part of their acute nonparalytic polio to experience this type of fatigue. In addition, polio survivors who describe a fairly prominent fatigue can also complain about cognitive problems, such as impaired concentration and memory difficulties. Sleep disturbance, which is reported in polio survivors, can exacerbate their general fatigue. As fatigue is an unspecific symptom commonly occurring in other disorders, alternative diagnoses should be ruled out (e.g., depression, thyroid dysfunction, anemia, other inflammatory diseases, or vitamin B 12 deficiency).
Pain
Pain is common among people with PPS and often the symptom that drives them to seek medical help. It has been shown that 50% to 90% of those with PPS experience pain. Pain is common in the shoulders, lower back, legs, and hips and is usually most pronounced in the legs. It is associated with depression and fatigue and can also affect sleep. Not everyone experiences pain, however, and many suffer from mild or no pain. In general, though, increasing pain is related to a lower perceived life satisfaction. Pain can emanate from a joint, a muscle, ligaments, tendons or tendon sheaths, muscle and tendon insertions, and bursae close to a joint. The reason for this is usually the weakness that occurs as a result of muscle atrophy in PPS, which leads to muscle imbalance, stress, and overload and incorrect posture. Pain in PPS can be aching, burning, or cramping in the muscles. Joint pain commonly occurs as a result of the gradual development of osteoarthritis. Osteoarthritis can affect joints in parts of the body with muscle weakness resulting from polio but also affects parts of the body not affected by polio because of compensatory overload. Osteoarthritis usually occurs in hip, knee, and foot joints; typical symptoms are pain under strain, but pain at rest is also common.
Respiratory Problems
During the initial polio infection, breathing could be affected as a result of paralyzed respiratory muscles. This was treated with a ventilator for a longer or shorter time, and some have used a ventilator ever since their polio infection, whereas most improved and managed without it. These people may later in life experience new weakness in their respiratory muscles that can lead to an inability to maintain normal carbon dioxide levels in the blood because of reduced breathing volumes. This so-called underventilation is exacerbated by obesity and worsened by other restrictive lung diseases. However, polio-related respiratory problems occur in less than 10% of those with PPS. People with PPS-related underventilation can complain of morning headache, daytime tiredness, problems with concentration, restless sleep, waking up several times, nightmares, difficulty getting up in the morning, and increased breathlessness during and after exertion.
Swallowing
Swallowing problems occur in those who had bulbar poliomyelitis that affected the swallowing muscles during the initial infection. Usual complaints are feelings of choking, gagging or coughing, and irritation in the throat or a feeling of a lump in the throat. Some people will also complain of voice problems, especially dysphonia.
Cold Intolerance
Cold intolerance is a feeling of coldness in the arms and legs and a general inability to thermoregulate. Cold intolerance may be caused by damage to the part of the brain that regulates body temperature, effects on nerves to arms and legs, or reduced muscle mass. It may also be exacerbated by other medical conditions, such as peripheral vascular disease.
Physical Examination
The findings during a clinical, musculoskeletal, and neurologic examination should support the diagnosis of a lower motor neuron disease process. This includes absent or diminished reflexes, decreased muscle tone, and atrophy (symmetric or asymmetric) and weakness of the muscles in the limbs or trunk. Sensory deficits are not part of PPS, but median and ulnar nerve entrapments are common in polio survivors; therefore, it is important to search for symptoms and signs of sensory disturbances in the hands.
Biomechanical symptoms and signs may also occur from musculoskeletal abnormalities in the lower extremities. This, in turn, is a result of contractures due to muscle weakness (hip and ankle), weakness of the quadriceps causing genu recurvatum at the knee, and reduced joint range of motion without apparent contributing weakness (common in the cervical spine and shoulders). Leg length discrepancies are common and may lead to scoliosis and kyphosis and pain from the spinal column.
Manual muscle testing is a quick and useful assessment of function. However, the occurrence and distribution of muscle weakness, as a hallmark of PPS, can be anything from obvious to subtle. It is therefore not always possible to rule out PPS solely by a clinical examination of muscle strength.
Visual assessment of gait and gait disturbances is a starting point for more mechanistic evaluations. Also, specific areas of the body that are reported as painful should be examined. Seating posture, turning, rising from a chair, and stair climbing are specific movements that can be affected, leading to pain, and may require interventions and corrections.
Fatigue is a common symptom and may be associated with other disorders. Therefore, it is important to detect possible signs and symptoms of, for example, depression and sleep disorders. Respiratory problems should also be ruled out by a general physical examination complemented by a basic spirometer examination. Assessment of peripheral pulses and edema is also important.
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