Poliomyelitis is a neurotropic enterovirus that causes paralysis through motor neuron destruction, muscle denervation, and atrophy. Indigenously acquired wild poliovirus was eradicated from the United States in 1979 and from the Western Hemisphere in 1991. However, the disease is still endemic in India, Pakistan, Afghanistan, and Nigeria.82 Postpolio syndrome, also called postpoliomyelitis progressive muscular atrophy, is an important sequela of acute poliomyelitis. This disorder is characterized by the recurrence of motor symptoms, following a latent period of several decades, after the resolution of the motor symptoms caused by the initial infection.
Mass immunization with the inactivated poliovirus vaccine or attenuated oral poliovirus vaccine has dramatically reduced the incidence of polio, but polio outbreaks still occur in populations that are not consistently or adequately immunized. Immunocompromised patients are at greater risk for contracting polio after exposure to children who were vaccinated with the attenuated oral poliovirus vaccine. With the use of attenuated oral poliovirus vaccine, some immunized children will develop polio, as will some young adults who are exposed to children who have been vaccinated with the attenuated oral poliovirus vaccine; immunocompromised patients are at greater risk for this. In developing countries, recent intramuscular injections, tonsillectomy, and strenuous exercise all are associated with increased polio infection severity.
Postpolio syndrome is expected to affect up to 100,000 of the 250,000 U.S. adults with a history of polio. Because most cases of polio occurred before mass immunization, patients diagnosed now with postpolio syndrome most likely will be >50 years old. Disease onset is 20 to 35 years after the initial infection. Although postpolio syndrome most often occurs after a stable, disease-free period of 20 to 30 years, current retrospective reviews claim 35 years.83 There are risk factors that predict an earlier onset of postpolio syndrome. These include advanced age at the time of initial polio infection, greater residual motor disability, residual bulbar or respiratory signs, and the occurrence of recent injuries that require limb immobilization. Postpolio syndrome is a diagnosis of exclusion.84
In developed countries, the viral transmission of polio is oral to oral, whereas in developing countries, where the sanitation is poor, the transmission is fecal to oral. Acutely, the polio enterovirus enters the body through the GI tract and reproduces in the GI lymphoid tissue, termed gut-associated lymphoid tissue. Oral secretion of the virus takes place for several days, whereas stool excretion can last for several weeks.
At a critical concentration, the virus spreads to the large motor nuclei of the spinal cord, the brainstem, and the reticular formation. The vestibular and brainstem motor nuclei, hypothalamus, thalamus, cerebellum, and precentral motor cerebral cortex also can be infected by the poliovirus. There is loss of infected neurons. Neuron loss then causes a cycle of muscle denervation and reinnervation, resulting in loss of muscle function.
The cause of the postpolio syndrome is unknown. The motor neuron degeneration is thought to be a result of dysfunction in the individual nerve axons in surviving motor neurons.
Polio infection is asymptomatic in >90% of cases. The majority of symptomatic polio infections involve only a minor viral illness that causes no paralysis, termed abortive polio. After an incubation period of a few days, symptoms may include fever, malaise, headache, sore throat, and GI symptoms. Some of the patients who experience the minor viral illness, especially young children, may develop aseptic meningitis as the infection resolves. Only 1% to 2% of all poliovirus infections result in the major illness associated with neurologic involvement. Often there is resolution of the minor viral illness symptoms before development of neurologic symptoms, so that it is difficult to identify the preceding minor viral illness. Muscle pain, stiffness, and weakness during the early viral syndrome may be premonitory of later paralysis.
When the major illness occurs, most commonly the spinal cord anterior horn cells are affected, causing asymmetric proximal limb weakness, especially in the lower extremities. Flaccid and weak muscles, absent tendon reflexes, and fasciculations characterize spinal polio. Although polio patients note pain, paresthesias, and transient sensory abnormalities, sensory deficits are usually not found on clinical examination. Maximal paralysis usually occurs within 5 days, and muscle wasting then occurs over several weeks. Autonomic dysfunction, including sweating disturbances, urine retention, delayed gastric emptying, and constipation, is commonly found. Most spinal polio patients will demonstrate improved motor function, with resolution of the paralysis occurring within the first year after the acute infection.
Up to 20% of polio patients with paralysis will develop bulbar polio, which can cause speech, swallowing, facial muscle, and extraocular muscle dysfunction. Acute polio infection also can cause encephalitis and can disturb the reticular formation, resulting in cardiac dysrhythmias, blood pressure alterations, hypoxia, and hypercarbia. Patients who survive the acute episode of encephalitis normally recover without residual effects.
Consider acute paralytic poliomyelitis whenever an at-risk patient develops an acute febrile illness, aseptic meningitis, and asymmetric flaccid paralysis associated with the loss of deep tendon reflexes and normal sensation. As with other causes of aseptic meningitis, the cerebrospinal fluid reveals pleocytosis during the first week after paralysis onset. The cerebrospinal fluid white cell count can elevate into the hundreds, with a predominance of neutrophils early in the disease course. Although the poliovirus can be cultured from the cerebrospinal fluid early in the disease course, throat and rectal swabs provide a greater yield. When a particular viral serotype is identified, serial serum antibody titers can be used to verify the cultures.
The most important cause of paralysis on the differential diagnosis that must be considered and excluded is Guillain-Barré syndrome, which, unlike the acute polio infection, causes more symmetric muscle weakness. Acute paralysis can result from peripheral neuropathies caused by infectious mononucleosis, Lyme disease, or porphyria. Paralysis also can result from inflammatory myopathies, electrolyte abnormalities, toxins, or other viruses, such as coxsackieviruses, mumps, echoviruses, and nonpolio enteroviruses. Paralysis also can result from acute spinal cord compression, vascular lesions, and transverse myelitis, all of which should produce a sensory level and sphincter disturbances. In children, it is necessary to exclude spinal muscular atrophy, which can be undiagnosed until it is manifested by dramatic limb weakness caused by an acute febrile illness.
Patients with postpolio syndrome complain of muscle fatigue, joint pain, worsening of skeletal deformities, or weakness in muscles that were spared during the initial viral infection.85 When muscle weakness is observed, atrophy, pain, and fasciculations may be noted both in previously unaffected muscle groups and in those previously involved. Patients may also develop new bulbar, respiratory, or sleep difficulties. For example, laryngeal muscle weakness can cause progressive dyspnea, dysphagia, and/or hoarseness. Some patients complain of abnormal movements in sleep that disturb normal sleep, requiring therapy with benzodiazepines or dopaminergic drugs.86 These symptoms occur independently of any concurrent neurologic, orthopedic, psychiatric, or systemic medical illness.
To diagnose postpolio syndrome, the patient should have a history of acute paralytic poliomyelitis with stable recovery of motor function associated with residual muscle atrophy, weakness, and areflexia with normal sensation in at least one limb. Additionally, there should be new muscle symptoms or weakness not attributable to an acute injury, neuropathy, radiculopathy, or systemic, neurologic, or psychiatric illness.
Treatment of the new muscle weakness seen with postpolio patients is primarily symptomatic, with the use of analgesic and anti-inflammatory medications. Most patients with postpolio syndrome benefit from muscle training87 and daily exercise.88 An additional therapeutic option is lamotrigine (Lamictal). When used in conjunction with an exercise routine, lamotrigine may improve the quality of life in postpolio patients.89
Acknowledgments: The authors would like to thank Edward P. Sloan for his work on previous editions of this chapter.