Version May 2024
INTRODUCTION — Polioviruses are neurotropic enteroviruses that target motor neurons in the spinal cord and brainstem causing poliomyelitis (often referred to as "polio"). As a result of eradication efforts, polio no longer poses the public health threat that it once did; however, limited areas of endemic wild-type poliovirus transmission remain, and rare cases of oral polio vaccine-associated poliomyelitis continue to occur.
Post-polio syndrome (PPS) is a condition characterized by new or progressive muscle weakness that develops in the decades following a poliomyelitis infection. PPS occurs in up to one-half of patients with prior poliomyelitis infection.
The clinical features, diagnosis, and management of both poliomyelitis and PPS are reviewed here. Issues related to poliovirus vaccination and global eradication are reviewed separately. (See "Poliovirus vaccination" and "Global poliomyelitis eradication".)
Other causes of acute flaccid paralysis, including acute flaccid myelitis, are reviewed elsewhere. (See "Acute flaccid myelitis".)
POLIOMYELITIS
Virology and forms of illness — Human enteroviruses contain a single positive-strand ribonucleic acid (RNA) genome and are subdivided into four species by genetic homology: human enterovirus types A, B, C, and D. Polioviruses belong to the human enterovirus C species [1]. There are three poliovirus serotypes, each of which can cause motor neuron disease. Most paralytic disease in the prevaccination era was caused by poliovirus serotype 1 (WPV1).
Acute poliomyelitis may result from infection with either naturally occurring (wild) polioviruses or with oral polio vaccine (OPV) related viruses. OPV-related infections occur in one of the following forms:
●Vaccine-derived polioviruses (VDPV) – VDPV are polioviruses that have that have emerged in regions that use one of the Sabin OPV strains. These strains circulate due to low population immunity, acquire biologic properties similar to those of naturally occurring wild-type polioviruses via genetic reversion, and cause poliomyelitis illness.
VDPV transmission can lead to outbreaks of poliomyelitis, especially in areas of low population immunity. Effective individual- and community-level vaccination efforts are part of the Global Polio Eradication Program to reduce the risks of VDPV. (See "Global poliomyelitis eradication", section on 'Vaccine-derived polioviruses'.)
●Vaccine-associated paralytic poliomyelitis (VAPP) – VAPP occurs when an OPV virus strain reverts to neurovirulence during replication in the gastrointestinal tract of a susceptible host. It may occur in recently vaccinated infants, individuals with B cell immunodeficiency, and direct contacts of OPV recipients.
VAPP is rare (occurring in approximately 1 person per 2.5 million vaccine doses). In resource-rich settings, VAPP occurs most commonly after the first OPV dose; in resource-limited settings, VAPP may occur in children who have received multiple prior OPV doses [2]. Approximately one-third of reported VAPP cases follow transmission to a household or community contact of the vaccinated infant.
Illness and other adverse effects related to OPV are discussed in greater detail separately. (See "Poliovirus vaccination", section on 'Adverse effects'.)
Transmission and pathogenesis — Poliovirus is highly infectious; it is transmitted by the fecal-oral route or by pharyngeal secretions [3]. The virus may persist in stool for as long as six weeks and may be shed in individuals with or without symptoms.
Entry via the oral route is followed by replication in the lymphatic tissues of the oropharyngeal and gastrointestinal tracts. A transient asymptomatic viremia occurs, with viral spread to the reticuloendothelial system.
The mechanism of poliovirus spread to the central nervous system (CNS) is not well understood; it may occur via passage of the virus through the blood-brain barrier, or via retrograde axonal transport from muscle to peripheral nerves, then the spinal cord and brain.
After reaching the CNS, viral replication in spinal motor neurons results in cell death and paralysis of muscle fibers supplied by the affected motor neuron. Involvement of cranial nerves and thoracic muscles can lead to difficulty swallowing and respiratory insufficiency [4]. Spread of the virus to neighboring motor neurons may occur by transneuronal spread, independent of axonal transport, in a retrograde transport-dependent fashion [5].
Epidemiology
●Status of global eradication efforts – The Global Polio Eradication Program has reduced the number of WPV1 cases to very small numbers. However, eradication has been challenged by spread of circulating type 2 vaccine-derived polioviruses (cVDPV2) across sub-Saharan Africa and elsewhere [6]. Many countries in Asia and Africa remain at risk of cVDPV2 spread from endemic areas or reintroduction of WPV1 infection because of low population immunity due to inadequate immunization. Issues related to global polio eradication efforts are discussed separately. (See "Global poliomyelitis eradication".)
●United States and other resource-rich settings – In the United States, no endemic cases of polio caused by wild poliovirus have been observed since 1979, and the World Health Organization Region of the Americas was declared polio-free in 1994 [7]. However, polioviruses (wild and vaccine-derived) have been brought into the United States by travelers [8,9].
In June 2022, poliovirus was confirmed in an unvaccinated immunocompetent adult resident of Rockland County, New York hospitalized with acute flaccid lower limb weakness [9]. Circulating VDPV2 was detected in the patient’s stool and was also identified from wastewater samples in two neighboring New York counties along with genetically related OPV2 viruses, reflecting community transmission [10]. The patient had not traveled internationally during the presumed exposure period; therefore, stool detection of cVDPV2 suggests that transmission originated in a person within the United States who was exposed to type 2-containing OPV abroad. OPV was removed from the routine immunization schedule in the United States in 2000 and in the United Kingdom in 2004.
Circulating VDPV2 has also been detected in 2022 from wastewater samples in Israel and the United Kingdom [11,12]. Issues related to environmental surveillance are discussed further separately. (See "Global poliomyelitis eradication" and "Global poliomyelitis eradication", section on 'Surveillance'.)
Unvaccinated individuals remain at risk for paralytic poliomyelitis if they are exposed to wild or vaccine-derived poliovirus; all individuals should stay up to date on recommended poliovirus vaccination. (See "Poliovirus vaccination".)
Clinical manifestations — Most poliovirus infections are inapparent. For other patients, symptomatic illness presents in the following ways:
●Mild illness – Approximately 4 to 8 percent of infected individuals experience a self-limited illness after an incubation period of three to six days; systemic symptoms may include fever, headache, and sore throat and fatigue and typically resolve within one to two days without further manifestations [13].
●Severe illness – Approximately 1 to 2 percent of infected individuals develop a more severe illness, often with meningitis. Severe illness can be categorized by the presence of motor symptoms:
•Nonparalytic polio – Nonparalytic polio refers to severe illness in the absence of motor weakness. Symptoms typically include fever, headache, vomiting, and meningismus. Symptoms begin after an incubation period of 7 to 21 days and may or may not be preceded by mild illness. CSF examination at this stage may demonstrate moderate pleocytosis with an elevated protein concentration. (See 'Clinical evaluation' below.)
Nonparalytic polio typically resolves within one to two weeks; however, it progresses to paralytic polio in a minority of patients.
•Paralytic polio – Paralytic polio consists of acute flaccid weakness with pain due to anterior horn cell injury. The onset of pain and weakness may either coincide with or follow the onset of severe illness [5,13].
Approximately 0.5 to 0.05 percent of infected individuals (1 in 200 to 1 in 2000 individuals) develop paralytic polio after the virus infects the spinal cord [14].
The distribution and extent of weakness ranges from one muscle or group of muscles to quadriplegia and respiratory failure. Muscle tone is reduced, nearly always asymmetrically. Proximal muscles are usually affected more than distal muscles, and legs more commonly than arms. Reflexes are decreased or absent. The sensory examination is almost always normal.
Weakness typically worsens over two to three days; sometimes worsening can progress for up to a week. Bulbar involvement occurs in 5 to 35 percent of patients, producing dysphagia, dysarthria, and difficulty handling secretions. Respiratory failure may occur, requiring mechanical ventilation [13,15]. Motor recovery occurs over months and is often incomplete. (See 'Outcomes' below.)
Diagnosis
Overview — The diagnosis of poliomyelitis should be suspected in patients with aseptic meningitis and acute flaccid weakness. In addition, suspicion should be increased for symptomatic patients in the setting of epidemiologic exposure, particularly among unvaccinated individuals. (See 'Epidemiology' above.)
The diagnosis of poliomyelitis is established by identifying the virus from stool samples, oropharyngeal swabs, and/or cerebrospinal fluid.
Patients with suspected poliomyelitis should be isolated while undergoing diagnostic evaluation. (See 'Infection control' below.)
Clinical evaluation — For patients with acute flaccid weakness, we pursue diagnostic evaluation to identify poliovirus and to evaluate for other conditions with similar clinical presentations (table 1). Because of the rarity of poliomyelitis in resource-rich settings, much of the diagnostic evaluation in these regions requires thorough evaluation for other more common causes of acute flaccid weakness. (See 'Differential diagnosis' below.)
Diagnostic testing typically includes:
●Laboratory testing for enteroviruses
•Stool samples – Two stool samples should be obtained at least 24 hours apart during the first 14 days after onset of limb weakness. These should be sent to regional/state/local health departments for initial enterovirus testing. Testing consists of cell culture and reverse-transcriptase polymerase chain reaction (RT-PCR) for polio and nonpolio enteroviruses [16].
•Oropharyngeal swabs – Two swabs should be obtained at least 24 hours apart during the first 14 days after onset of limb weakness. These should be sent to regional/state/local health departments for initial enterovirus testing.
●Other laboratory testing – Laboratory testing for other causes of acute flaccid paralysis (eg, West Nile virus infection, myasthenia gravis) is typically performed when a history of suspected exposure to poliovirus is uncertain to evaluate for other infectious or inflammatory conditions (table 1).
●Cerebrospinal fluid (CSF) analysis – CSF analysis is performed for all patients with meningitis or paralytic illness to identify polioviruses and exclude other etiologies.
•Composition – The CSF in poliomyelitis demonstrates a moderate pleocytosis initially characterized by a neutrophil predominance, followed by a later shift to predominantly lymphocytes. The CSF protein is usually elevated. (See "Aseptic meningitis in adults", section on 'Viral meningitis'.)
•Virus detection – A CSF sample should be sent for detection of poliovirus by viral culture or PCR amplification of poliovirus RNA whenever stool and oropharyngeal swab testing is negative. However, poliovirus is detected in CSF in fewer than 30 percent of patients with poliomyelitis. PCR is more sensitive than culture. (See "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention", section on 'Laboratory diagnosis'.)
●Neuroimaging – The clinical presentation may be sufficient to diagnose a pure lower motor neuron syndrome. However, magnetic resonance imaging (MRI) of the brain and spine with contrast may be warranted for patients with upper motor neuron signs or symptoms to assess for causes of acute myelopathy or radiculopathy. As examples, patients with acute flaccid myelitis or spinal cord infarction may have T2 hyperintensities in the spinal gray matter and/or lower brainstem. In addition, MRI may be useful for patients with poliomyelitis to assess the extent of spinal cord inflammation. (See "Acute flaccid myelitis", section on 'Evaluation'.)
●Electrodiagnostic studies – Electrodiagnostic studies consisting of nerve conduction studies (NCS) and electromyography (EMG) are typically performed for patients with paralytic symptoms to exclude alternative etiologies and to identify selective injury to motor neurons consistent with polio. In addition, they may be helpful for patients with poliomyelitis to assess the severity of nerve impairment.
On NCS, compound motor action potentials have low amplitude suggestive of motor axonal loss and motor conduction velocities are normal to mildly slowed. The sensory nerve conduction studies are usually normal.
On EMG, the decreased number of axons manifests initially as decreased recruitment in weak muscles. Within 10 to 21 days following the onset of the disease, needle EMG testing shows spontaneous denervating potentials (ie, fibrillation potentials and positive waves); as the reinnervation process has not yet started, the motor unit action potential morphology remains normal.
After approximately two months, as reinnervation occurs, the motor unit territory of the surviving axons increases as a result of nerve sprouting, and the morphology of the motor unit action potential changes, with increases in amplitude, duration, and number of phases.
Differential diagnosis — The differential diagnosis of poliomyelitis includes other infectious and noninfectious causes of acute flaccid paralysis (table 2). The conditions that most resemble acute flaccid paralysis from poliomyelitis include other infectious causes of acute flaccid paralysis (non-polio enteroviruses or West Nile virus) and Guillain-Barré syndrome (GBS). Consideration of GBS is important since this condition generally responds to treatment with intravenous immune globulin (IVIG) and plasma exchange.
●Infectious causes
•Non-polio enteroviruses – Acute flaccid myelitis (AFM) is a syndrome of acute motor neuron weakness caused by non-polio enteroviruses including enterovirus D68, enterovirus A71, echoviruses, and some coxsackievirus serotypes. AFM shares common clinical and pathophysiologic features with poliomyelitis [17]. (See "Acute flaccid myelitis" and "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention", section on 'Central nervous system infections'.)
•West Nile virus (WNV) – WNV is a mosquito-borne flavivirus that can cause acute flaccid paralysis with or without meningoencephalitis. (See "Clinical manifestations and diagnosis of West Nile virus infection".)
•Other viruses – Other viral infections that rarely cause acute flaccid paralysis include varicella zoster virus [18] and rabies [19]. (See "Epidemiology, clinical manifestations, and diagnosis of herpes zoster", section on 'Other neurologic complications' and "Clinical manifestations and diagnosis of rabies", section on 'Paralytic rabies'.)
•Bacterial infection – Other infections, such as toxigenic diphtheria (due to Corynebacterium diphtheria) and botulism (due to Clostridium botulinum), may produce acute flaccid paralysis. (See "Clinical manifestations, diagnosis, and treatment of diphtheria" and "Botulism".)
●Noninfectious causes
•Guillain-Barre syndrome (GBS) – GBS is an acute immune-mediated polyneuropathy; it usually can be distinguished from poliomyelitis by its symmetric motor weakness, the presence of sensory symptoms, lack of preceding aseptic meningitis, absence of CSF pleocytosis, and the presence of multifocal demyelination on electrodiagnostic testing. The electrodiagnostic findings are less helpful early in the course, when demyelinating findings may not yet have developed, or with axonal forms of the condition. (See "Guillain-Barré syndrome in adults: Pathogenesis, clinical features, and diagnosis" and "Guillain-Barré syndrome in children: Epidemiology, clinical features, and diagnosis".)
•Spinal cord disorders – Disease at other levels of the neuraxis must also be considered. Spinal cord disorders such as transverse myelitis, spinal cord infarction, and cord compression can produce weakness. Upper motor neuron findings are typically present but may be absent initially. (See "Disorders affecting the spinal cord".)
•Acute intermittent porphyria – Peripheral motor neuropathy may be a feature of acute intermittent porphyria. Muscle weakness often begins proximally in the legs but may involve the arms or the distal extremities. Motor neuropathy may also involve the cranial and/or phrenic nerves leading to bulbar paralysis and respiratory impairment and may result in death if undetected. (See "Acute intermittent porphyria: Pathogenesis, clinical features, and diagnosis".)
•Mononeuritis multiplex – Mononeuritis multiplex is a form of neuropathy that may present with pain and weakness. However, it is typically also associated with sensory symptoms and signs, and weakness is often restricted to the distribution of specific peripheral nerves. (See "Clinical manifestations and diagnosis of vasculitic neuropathies".)
•Disorders of neuromuscular transmission – Disorders of neuromuscular transmission such as myasthenia gravis or Lambert-Eaton myasthenic syndrome may produce acute flaccid paralysis. These disorders are typically symmetric, associated with normal CSF, and characterized by abnormal findings on repetitive nerve stimulation electrodiagnostic testing. They are usually not associated with a systemic illness. (See "Clinical manifestations of myasthenia gravis" and "Lambert-Eaton myasthenic syndrome: Clinical features and diagnosis" and "Overview of neuromuscular junction toxins".)
•Inflammatory myopathies – Inflammatory neuropathies such as polymyositis and inclusion body myositis frequently cause motor weakness. However, patients with inflammatory myopathies usually describe a gradual onset of weakness over several months, unlike the more acute onset of weakness with poliomyelitis. In addition, symptomatic patients with myopathy typically have a high serum creatine kinase (CK) level and no prodromal illness. Patients may also have arthropathies and skin findings with several forms of inflammatory myopathy. (See "Juvenile dermatomyositis and other idiopathic inflammatory myopathies: Epidemiology, pathogenesis, and clinical manifestations" and "Clinical manifestations of dermatomyositis and polymyositis in adults" and "Clinical manifestations and diagnosis of inclusion body myositis".)
•Rhabdomyolysis – Patients with rhabdomyolysis may experience rapidly developing quadriparesis, but in association with severe muscle pain, symmetry, a dramatically elevated serum CK level, myoglobinuria, and normal CSF. (See "Rhabdomyolysis: Clinical manifestations and diagnosis".)
Management — Management of poliomyelitis is supportive, including pain management and physical therapy. Respiratory failure may develop, requiring mechanical ventilation. Patients with bulbar involvement require close monitoring of cardiovascular status because of the association with blood pressure fluctuations, circulatory collapse, and autonomic dysfunction [3,13,15,20]. Such patients may require intubation for airway protection.
There are no approved antiviral therapies for poliomyelitis. Experimental antiviral drugs that have been evaluated in enterovirus infections are discussed separately. (See "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention", section on 'Antiviral therapy for severe cases'.)
Prevention
Vaccination — Issues related to poliovirus vaccination are discussed separately. (See "Poliovirus vaccination".)
Infection control — Patients with known or suspected poliomyelitis should be isolated in a room with a private bathroom, if possible. Standard, droplet, and contact precautions should be used. (See "Infection prevention: Precautions for preventing transmission of infection".)
Only healthcare personnel with evidence of complete polio vaccination should care for patients with known or suspected poliomyelitis. (See "Poliovirus vaccination".)
Outcomes — Approximately two-thirds of patients with acute flaccid paralysis from poliomyelitis do not regain full strength. The more severe the acute weakness, the greater the likelihood of residual deficits. Chronic bulbar sequelae are rare. In the epidemic era the mortality was 5 to 10 percent, and approached 50 percent for those with bulbar involvement because of cardiovascular and respiratory complications [3,13,15,20].
In addition to weakness, patients with polio may have long-lasting effects including chronic pain, contractures, depression, fatigue, sleep problems, and a host of other manifestations that may adversely impact quality of life [21].
POST-POLIO SYNDROME — Post-polio syndrome (PPS) is characterized by new or progressive muscle weakness with functional deterioration after a prolonged period of stability in patients with a history of acute flaccid paralysis from polio. PPS usually occurs decades after the initial infection.
Epidemiology — Estimates of the incidence and prevalence of PPS vary greatly by the criteria used for establishing the diagnosis. Approximately 50 percent of patients may report new symptoms related to prior polio such as weakness, pain, fatigability, or concentration difficulty [22]. However, if new, progressive weakness is included as a criterion, the frequency of PPS drops to approximately 20 to 30 percent of patients with prior polio [23].
On average, the onset of new symptoms occurs approximately 35 years after the initial polio episode; onset ranges between 8 to 71 years [24-27]. PPS occurs sooner in patients with more severe initial illness [26,28].
Risk factors — Risk factors for PPS include [24,28-32]:
●Severe weakness during the acute paralytic infection
●Older age at which acute polio occurred
●Female sex
●Chronic gait impairment following acute recovery
Pathogenesis — The cause of progressive neurologic deterioration in PPS is unknown. The main theories of pathogenesis involve progressive degeneration of reinnervated motor units, increased metabolic demand of reinnervated motor units with subsequent neuromuscular junction dysfunction, persistence of poliovirus in neural tissue, and induction of autoimmunity with consequent destruction of neural structures.
●Motor unit degeneration – Acute paralytic poliomyelitis leads to a loss of motor neurons with subsequent denervation. With functional recovery, incomplete compensation for initial denervation occurs by reinnervation of the muscle fibers through collateral sprouting [29]. This results in surviving peripheral nerves supplying a greater number of muscle fibers (ie, motor unit enlargement). Cerebral reorganization of gray and white matter tracts following peripheral denervation may also contribute to motor recovery after polio [33]. The new weakness characteristic of PPS may result when these compensatory mechanisms are overwhelmed by neurodegeneration with a delayed loss of additional motor axons.
The possibility that motor neuron degeneration may underlie the motor unit loss was supported by the findings of a small case-control study in patients with PPS that found increased cerebrospinal fluid (CSF) expression of proteins that are known to be involved in different pathways mediating neurodegeneration, such as apoptosis [34]. These proteins include gelsolin, hemopexin, peptidylglycine alpha-amidating monooxygenase, glutathione synthetase, and kallikrein 6. Muscle biopsy studies show that pathologic angulated fibers become more frequent as a function of the time elapsed since the acute episode of polio [35].
●Neuromuscular junction dysfunction – Another possible underlying cause of PPS is the failure of neuromuscular transmission. The expanded architecture of enlarged, reinnervated motor units increases baseline metabolic demand, which can lead to instability of reinnervated neuromuscular junctions. Electrophysiologic studies suggest that the most extensively reinnervated motor units after polio are more likely to become unstable later in life, with ultimate failure of neuromuscular transmission [36,37].
●Persistence of poliovirus in the nervous system – The presence and reactivation of persistent poliovirus has been speculated to account for the progression of motor neuron degeneration in some patients [38]. Poliovirus and other enteroviruses may persist in the central nervous system (CNS) as well as systemically in children with certain B cell immunodeficiencies [24]. (See "Enterovirus and parechovirus infections: Epidemiology and pathogenesis".)
Studies in tissue culture have shown that poliovirus variants can persist in neurons in a latent state [39]. Support for the persistent poliovirus hypothesis was provided by a study demonstrating poliovirus antibodies and poliovirus-sensitized cells in the CSF of patients with PPS [40]. However, other studies have failed to demonstrate poliovirus antibodies in the CSF of patients with PPS [38,41,42], and most studies that have sought poliovirus RNA in the CSF of patients with PPS by polymerase chain reaction (PCR) have been negative or inconclusive [43,44].
●Inflammation and induction of autoimmunity – Support for an inflammatory or immune-mediated mechanism for PPS comes from an autopsy study demonstrating inflammation in the spinal cord of seven patients with PPS [45]. Perivascular and parenchymal lymphocytic infiltrates as well as neuronal degeneration with active gliosis were noted, and these changes were more prominent in the three patients with clearly progressive weakness.
Further evidence comes from the observations that expression of certain proinflammatory cytokines is increased in CSF (tumor necrosis factor-alpha and interferon-gamma) and serum (tumor necrosis factor-alpha, interleukin 6, and leptin) of patients with PPS [46,47]. Increased expression of enzymes of the E2 prostaglandin pathway in the muscles affected by PPS has also been described [48]. The finding of oligoclonal bands in the CSF also has been interpreted to support the autoimmune hypothesis, although the presence of inflammation does not indicate whether the immune response is a primary cause of disease or merely a reaction to another cause such as persistent infection [42].
Clinical manifestations — PPS is a disorder with neurologic and musculoskeletal components. Most commonly, symptoms include progressive weakness, fatigue, and pain in the muscles or joints. Symptoms most commonly occur decades following recovery from acute poliomyelitis.
As many of these symptoms are nonspecific (especially fatigue), PPS can be difficult to diagnose unless multiple musculoskeletal or neurologic findings are present. (See 'Diagnosis' below.)
●Progressive muscle weakness – Progressive muscle weakness occurs in most patients with PPS [49-51]. Some patients with PPS experience generalized weakness, while others report focal loss of strength and decreased endurance during exercise [28]. The new weakness always occurs in muscles previously affected by the original disease. However, some patients may report new weakness in other muscles where previous involvement was subclinical and only detectable electrophysiologically [35]. Focal muscle weakness may be clinically apparent as limb weakness or respiratory and/or bulbar dysfunction.
•Somatic weakness – The distribution of the new weakness is often asymmetric and usually correlates with the severity of paralysis at the time of the acute poliomyelitis and with the extent of recovery [29]. As with the original disease, the new weakness can be proximal or distal and is often quite patchy. Focal atrophy and fasciculations accompany the weakness less than one-half of the time [51]. Muscle atrophy may occur in some patients with persisting weakness.
•Respiratory insufficiency – New muscle weakness may manifest as respiratory insufficiency, bulbar muscle weakness, and/or sleep apnea. The prevalence of sleep apnea in individuals with a history of poliomyelitis is up to 65 percent [52]. Respiratory insufficiency is usually due to peripheral motor unit dysfunction causing respiratory muscle weakness but occasionally is related to central hypoventilation because of residual damage from involvement of bulbar pathways in the lower brainstem.
Respiratory symptoms primarily occur in patients with severe residual respiratory impairment and with minimal reserve [53,54]. Respiratory failure is likeliest in patients who required respiratory support during the acute illness and who contracted polio when over 10 years of age. PPS patients with chronic respiratory impairment lose an average of 1.9 percent of vital capacity per year [55,56]. Respiratory failure may begin with nocturnal alveolar hypoventilation, and patients may require only nighttime respiratory support; however, more severely affected patients may ultimately require total ventilatory support. (See 'Respiratory function' below.)
•Dysphagia – New focal weakness of the bulbar musculature may also occur with PPS [57-61]. Chronic dysphagia after polio is due to weakness in pharyngeal and laryngeal muscles. Dysphagia may worsen in PPS, with patients reporting choking and coughing. Dysarthria may also occur as a result of facial weakness or vocal cord paralysis. (See "Approach to the evaluation of dysphagia in adults".)
●Fatigue – Fatigue is the most common symptom of PPS and occurs in approximately 80 percent of patients [49,62]. It is often described as a disabling, generalized exhaustion occurring suddenly after minimal exertion. General fatigue is distinct from muscle fatigue, which is characterized by loss of strength and decreased endurance during exercise.
Fatigue may be so severe as to impair concentration and mental functioning. With rest, symptoms abate, although sleep is often more effective than simple cessation of fatiguing activities.
The pathophysiology of fatigue in patients with PPS is uncertain. Studies investigating exercise-related failure of motor unit function have found abnormalities similar to those seen in myasthenia gravis in 10 to 20 percent of patients with PPS [63].
●Other features – Motor unit dysfunction can lead to other features of PPS from secondary musculoskeletal dysfunction. Clinical features such as joint and muscle pains and bony deformities usually reflect involvement of the bony skeleton, ligaments, and joints.
•Pain – Pain can develop in patients with a history of poliomyelitis for several reasons. Chronic weakness can lead to the development of spinal deformities (such as kyphoscoliosis), degenerative joint disease, and joint instability. New pain can occur in the absence of new weakness. If polio occurred in childhood, subsequent development of uneven limb size can contribute to long-term musculoskeletal degeneration, as can failing surgical interventions such as tendon transfers and joint fusions. Progression of these symptoms can further stress an asymmetric skeleton and may require use of ambulatory assistive devices.
•Restless legs syndrome – Neuropathy and spinal cord disorders are risk factors for restless legs syndrome (RLS), perhaps due to alterations in neurotransmission. RLS is also highly prevalent in patients with PPS [52,64-66]. A small case-control study found RLS was more common in patients with PPS than age- and sex-matched controls (64 versus 8 percent) [65]. The hallmark symptom of RLS is an often unpleasant or uncomfortable urge to move the legs. The symptom emerges during periods of inactivity, is most prominent in the evening, and is transiently relieved by movement. In some patients with PPS, fatigue that exhibits diurnal variation may represent early symptoms of RLS [66-68]. (See "Clinical features and diagnosis of restless legs syndrome and periodic limb movement disorder in adults".)
Some patients with PPS may also report other clinical symptoms including poor sleep quality, cognitive impairment, and cold intolerance [69-72].
Diagnosis — The clinical diagnosis of PPS is made in patients with a remote history of poliomyelitis who develop new, progressive muscle weakness. There are no pathognomonic findings that distinguish PPS from remote polio. New muscle weakness that involves the same muscles affected with the initial polio illness can is suggestive of PPS. However, correlating new symptoms with prior poliomyelitis symptoms may be challenging for patients who develop new diffuse weakness or have unknown prior symptoms.
Laboratory testing and electromyography is performed to exclude alternative conditions.
Diagnostic criteria — Diagnostic criteria for PPS were first described in 1972 [50] and subsequently revised in the 1980s [73] and 1990s [23]. The diagnostic criteria for PPS include [74,75]:
●A prior episode of poliomyelitis with evidence of residual motor neuron loss
●A period of at least 15 years after the acute onset of polio with neurologic and functional stability
●A gradual (or rarely abrupt) onset of new weakness and abnormal muscle fatigability that persists for at least one year
●Exclusion of other medical conditions that cause similar symptoms
Diagnostic evaluation — There are no confirmatory diagnostic tests for PPS. For most patients with progressive muscle weakness with suspected PPS, we perform limited laboratory testing and electromyography (EMG) to exclude alternative diagnoses and help confirm the diagnosis of PPS. Neuroimaging and muscle biopsy may also be helpful when the diagnosis remains uncertain despite initial testing.
●Laboratory studies – Routine blood tests, including the erythrocyte sedimentation rate, are normal in PPS. Nevertheless, blood tests are useful to help exclude systemic disease as the cause of the weakness and other symptoms. Exercise may result in dramatic elevations of creatine kinase (CK) in patients with polio-related weakness, but it is not clear that such increases distinguish between those with and without PPS [24,76,77].
We reserve cerebrospinal fluid (CSF) analysis for selected patients with rapid or severe weakness to identify alternative diagnoses such as chronic inflammatory demyelinating polyneuropathy. CSF in patients with PPS is typically normal, although mild protein elevation or oligoclonal bands are sometimes observed [24,42].
●Electromyography – EMG of patients with prior polio has provided insight into the pathophysiology of poliomyelitis but cannot clearly distinguish between patients with a history of polio and those with PPS [78-80]. Both patients with remote polio and those with PPS have motor unit changes on EMG from a loss of motor neurons. EMG is useful to confirm previous poliomyelitis, including its extent and severity, and to exclude other neuromuscular conditions such as amyotrophic lateral sclerosis, radiculopathy, neuropathy, and myopathy.
EMG studies show that patients with a history of polio have signs of chronic motor neuron loss both in areas with weakness and in areas that are clinically normal. These abnormalities include the presence of motor units that are increased in amplitude and prolonged in duration. Increased motor unit amplitude occurs as a compensatory change in response to ongoing loss of motor neurons or their axons.
In addition, motor unit number estimation, which measures the number of functional motor units innervating individual muscles, is abnormal in patients with a history of prior polio and in those with PPS [81,82]. There is no clear distinction between patients with prior polio or PPS with respect to either the number of motor units measured or the rate of decline of motor units.
Fibrillation potentials, which imply the presence of ongoing motor axon loss, theoretically should help distinguish patients undergoing new motor unit degeneration from stable patients with remote polio. However, these potentials are seen in only a minority of patients with prior polio, including both those with and without PPS [82]. Other measures that indicate instability of the motor unit are frequently abnormal in all patients with prior polio. While weak muscles show more frequent and more severe abnormalities than strong muscles, muscles with progressive weakness cannot clearly be distinguished from those with static abnormalities.
●Other testing – Additional testing is typically reserved for patients with atypical clinical features or uncertain diagnosis after initial laboratory testing and electromyography. Muscle ultrasound and/or biopsy may provide additional information to support the diagnosis of PPS.
•Neuroimaging – MRI of the spine without contrast may be performed for patients with limb weakness to exclude lumbar or cervical spinal stenosis or radiculopathy. Brain MRI may be warranted for patients with bulbar symptoms to exclude brainstem lesion as a cause to symptoms. Computed tomography (CT) is a less sensitive alternative imaging modality for patients unable to undergo MRI.
Quantitative muscle ultrasound is a noninvasive imaging modality that may be used to evaluate disease severity and progression in patients with PPS, though data are limited [83]. Ultrasound parameters such as echo intensity and muscle thickness may be used to measure muscle quantity and quality to distinguish healthy from diseased muscle. Muscle ultrasound may be useful for patients with PPS and severe weakness who have limited ability to participate in strength tests [83]. (See "Diagnostic ultrasound in neuromuscular disease".)
•Muscle biopsy – Muscle biopsy is typically used for selected patients with new weakness to assess for other nerve or muscle conditions. Muscle biopsy findings in PPS are nonspecific and may be observed in patients with a history of polio, with or without new progressive weakness.
Biopsy findings in patients with past poliomyelitis show evidence of chronic denervation and reinnervation as well as active denervation [24]. Chronic changes are manifested by fiber-type grouping, in which the normal mosaic of fiber types is replaced by a pattern where fibers of a single type are clumped together. This is the morphologic equivalent of the prolonged-duration, increased-amplitude motor units seen on EMG study.
One sign of active denervation is the presence of small, angulated fibers, which suggests degeneration of terminal motor axon sprouts. Another finding that supports active denervation is the expression of neural-cell adhesion molecules on the surface of muscle fibers [35,36]. Group atrophy, which suggests acute axonal destruction or motor neuron death, is seen less frequently in PPS than in amyotrophic lateral sclerosis but may be seen in both conditions.
Differential diagnosis — The differential diagnosis of PPS includes other conditions that may present with progressive muscle weakness and fatigue. These include [72,84-88]:
●Chronic inflammatory demyelinating polyneuropathy (see "Chronic inflammatory demyelinating polyneuropathy: Etiology, clinical features, and diagnosis")
●Amyotrophic lateral sclerosis (see "Clinical features of amyotrophic lateral sclerosis and other forms of motor neuron disease")
●Inflammatory myopathies (see "Overview of and approach to the idiopathic inflammatory myopathies")
●Hypothyroid myopathy (see "Hypothyroid myopathy")
●Cervical or lumbar spinal spondylosis with radiculopathies (see "Lumbar spinal stenosis: Pathophysiology, clinical features, and diagnosis" and "Cervical spondylotic myelopathy")
●Myasthenia gravis (See "Clinical manifestations of myasthenia gravis".)
●Polymyalgia rheumatica (see "Clinical manifestations and diagnosis of polymyalgia rheumatica")
●Fibromyalgia (see "Clinical manifestations and diagnosis of fibromyalgia in adults")
PPS is often distinguished from alternative diagnoses by compatible clinical features along with a history of a prior polio illness.
Management — The management of PPS is primarily symptomatic and supportive [89,90]. Care should be multidisciplinary to address musculoskeletal, respiratory, psychological, and/or social factors that may be present.
Symptomatic care
Musculoskeletal function
●New muscle weakness – Patients with PPS who have muscle weakness or muscle fatigue should engage in non-fatiguing exercise programs that use low-intensity sessions with short repetitions lasting several seconds, alternating with intervals of rest [89]. Overexertion or overuse should be avoided during these sessions. Supporting evidence for non-fatiguing physical therapy in patients with PPS includes several small, uncontrolled studies [91-97]. Muscle strengthening and aerobic exercise appear to improve functional outcomes for patients with PPS or prior polio [98]. One strategy uses pacing of physical activities with work-rest programs (eg, inserting two-minute rest periods after exhaustion or after six minutes of continuous work is performed) [89,91]. Work-rest interval programs have been associated with reductions in local muscle fatigue and improved recovery of strength and work capacity [91].
Aerobic training intensity should be tailored to stimulate a training effect but avoid muscular overload [99-101]. One proposed technique to accomplish this is by determining the anaerobic threshold, which is a direct indicator of aerobic capacity. This parameter can be identified in some patients with PPS by submaximal incremental exercise training on a cycle ergometer with heart rate monitoring and breath-by-breath gas exchange analysis [99]. In a 12-week randomized trial in 10 patients with PPS, moderate-intensity strength training improved muscle strength more than a no-training control condition [102].
There is no role for pyridostigmine or prednisone for improving strength or endurance in patients with PPS as clinical trials have failed to show a consistent benefit [103-106].
●Bulbar symptoms – Treatment for bulbar muscle weakness in PPS causing dysphagia and dysphonia has been evaluated only in small, uncontrolled studies. Dysphonia may be managed by instruction on voice-strengthening techniques and by using amplification devices [107]. Dysphagia may be improved by a program that teaches swallowing techniques [108]. (See "Oropharyngeal dysphagia: Clinical features, diagnosis, and management".)
●Generalized fatigue – For patients with PPS and generalized fatigue, management consists of energy conservation measures combined with an individualized, regular, nonfatiguing exercise program [109]. Measures to prevent or treat obesity and the use of assistive devices such as an orthosis, cane, or chair-lift are beneficial for conservation of energy and fall prevention.
Pharmacologic therapy also has been explored to treat fatigue and has anecdotally been reported to be useful for selected individuals. However, clinical trials and observational data have failed to show consistent efficacy of any single agent. A small trial of very low methodologic quality reported similar improvement in fatigue with amantadine or placebo [110,111]. Two small trials on modafinil failed to show improvements in fatigue or quality of life measures over placebo [112,113]. One trial of 30 patients with PPS reported modest improvements in reported fatigue with lamotrigine at two and four weeks, but longer-term benefits are unknown [114]. Amitriptyline has been postulated to improve fatigue in selected patients with PPS by controlling pain, but has not been studied in a controlled trial for this indication.
●Restless legs syndrome – Recognizing and treating RLS is important because it may be a highly prevalent cause of sleep-onset insomnia and fatigue in patients with PPS [66]. Pharmacotherapy for RLS includes dopamine agonists and gabapentinoid antiseizure medications. Some retrospective data on patients with PPS suggest that dopamine agonists can be effective in decreasing the severity of RLS symptoms [64]. The treatment of RLS is discussed in detail separately. (See "Management of restless legs syndrome and periodic limb movement disorder in adults".)
●Musculoskeletal pain and joint instability – Musculoskeletal pain and joint instability can be treated by decreasing mechanical stress on joints and muscles through pacing of physical activities, treatment of obesity, use of appropriate assistive devices (eg, orthoses, canes, walkers, and wheelchairs) [115,116], and judicious employment of nonsteroidal anti-inflammatory drugs [89].
Exercise studies evaluating patients with PPS generally have been performed under supervision with submaximal workloads and intermittent rest periods between sessions [75]. Using these principles, patients with PPS can obtain positive cardiorespiratory training without untoward effects on extremity function [75,117,118].
Respiratory function — Respiratory muscle weakness due to neuromuscular disease can cause insufficient ventilation, nocturnal hypoventilation, or ineffective cough. Respiratory insufficiency can also be due to bulbar muscle weakness.
Smoking cessation is recommended for patients with PPS. (See "Overview of smoking cessation management in adults".)
●Sleep-related breathing disorders – Treatment options for sleep-related breathing disorders (ie, obstructive sleep apnea, central sleep apnea, or nocturnal hypoventilation) associated with PPS include use of continuous and bilevel positive airway pressure ventilation [119,120]. (See "Obstructive sleep apnea: Overview of management in adults" and "Central sleep apnea: Treatment" and "Treatment and prognosis of the obesity hypoventilation syndrome".)
●Respiratory support – Patients with PPS and respiratory symptoms may require ventilatory support. Subjective clinical findings and objective pulmonary function tests are used together to determine when mechanical ventilation is indicated. The sniff nasal inspiratory pressure may have an increased sensitivity in patients with PPS and inspiratory muscle weakness compared with other noninvasive pulmonary function tests, such as forced vital capacity, maximum inspiratory pressure, and maximum expiratory pressure [121]. (See "Respiratory muscle weakness due to neuromuscular disease: Clinical manifestations and evaluation", section on 'Respiratory muscle strength testing'.)
Several reports suggest that the early introduction of noninvasive respiratory support is beneficial for patients with PPS who have respiratory dysfunction [56,75,119,120]. By using this approach, invasive ventilation (tracheostomy and permanent positive pressure ventilation) may sometimes be avoided [75]. (See "Respiratory muscle weakness due to neuromuscular disease: Management".)
●Vaccinations – Pneumococcal vaccination is recommended for all adults ≥65 years of age and other adults with chronic pulmonary disease, including patients with PPS and respiratory dysfunction. Influenza vaccination is also recommended for adults with neurologic conditions that can compromise handling of respiratory secretions. These issues are discussed separately. (See "Pneumococcal vaccination in adults" and "Seasonal influenza vaccination in adults".)
Bone health — Patients with muscle weakness and fatigue from PPS are at risk for falls and bone fractures. Physical therapy evaluation and use of assistive ambulatory aids may be helpful to prevent falls and injury for patients with PPS and musculoskeletal weakness. In a 2016 review of published studies on conditions associated with PPS, the prevalence of falls within the preceding year among patients with PPS ranged from 50 to 74 percent [122]. A population-based study reported the incidence of any fracture was 48 percent for patients aged 40 years or older with a history of poliomyelitis [123].
In addition, patients with PPS have a high rate of osteopenia and osteoporosis. A single center retrospective cohort of 50 patients with PPS found that nearly 40 percent had a bone fracture within the preceding five years, and more than 90 percent had osteoporosis or osteopenia [124]. Screening for osteoporosis is discussed in greater detail separately. (See "Screening for osteoporosis in postmenopausal women and men".)
Anesthetic considerations — Patients with PPS may have increased sensitivity to local anesthetics and to nondepolarizing muscle blockers resulting in a prolonged effect [125,126]. In addition, patients with neuromuscular disease may be susceptible to hyperkalemia when treated with succinylcholine. However, data to support these theoretical concerns are limited to individual case reports [127,128]. In one case report of cesarean delivery in a female with PPS, succinylcholine was used without complication [129].
Due to the potential risk of adverse effects from these agents along with the potential for impaired baseline respiratory function for many patients with PPS, we generally advise using short-acting anesthetic agents as needed for surgery or other procedures when other agents are available [126]. (See "Overview of anesthesia".)
No role for IVIG — Intravenous immune globulin (IVIG) has been proposed as a therapy for PPS based on the possible, but unproven role of autoimmunity in the pathogenesis. However, the available data do not support a benefit in patients with PPS, and there is no role for IVIG outside of clinical research studies [130-132].
Some observational studies reported IVIG was associated with improvements in pain or quality of life measures [133-135]. However, benefits have not been confirmed in clinical trials [136-138]. In a trial that included 142 adults with PPS, patients were assigned to two three-day infusions separated by three months of either IVIG or placebo [137]. At three months after the second infusion, there was improvement favoring IVIG for one of two primary outcomes (median strength in a selected study muscle), but this strength improvement was insufficient to reach the predetermined level considered clinically important. There was no difference between groups in the other primary outcome (quality of life). In another randomized trial of 20 patients with PPS, treatment with IVIG for two to four days led to an improvement in pain at three months compared with placebo but had no effect on strength and fatigue [138].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Polio".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Poliomyelitis (The Basics)" and "Patient education: Acute flaccid myelitis (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Poliomyelitis
•Transmission and epidemiology – Polioviruses are neurotropic enteroviruses that target motor neurons in the spinal cord and brainstem, causing poliomyelitis (often referred to as "polio"). Polioviruses are transmitted by the fecal-oral route or by pharyngeal secretions. (See 'Transmission and pathogenesis' above.)
Limited areas of endemic wild-type poliovirus transmission remain, and rare cases of oral polio vaccine (OPV)-associated poliomyelitis continue to occur. (See 'Epidemiology' above.)
•Clinical manifestations – Most poliovirus infections are asymptomatic. Approximately 4 to 8 percent of infected individuals experience a self-limited illness; symptoms may include fever, headache, sore throat, and fatigue. (See 'Clinical manifestations' above.)
Approximately 1 to 2 percent of people with poliovirus infection develop a more severe illness:
-Nonparalytic polio – Nonparalytic polio refers to severe illness (fever, headache, vomiting, and meningismus.) in the absence of motor weakness.
-Paralytic polio – Paralytic polio consists of acute flaccid weakness with pain due to anterior horn cell injury. The onset of weakness and pain may either coincide with or follow onset of severe illness. Approximately 0.5 to 0.05 percent of infected individuals (1 in 200 to 1 in 2000 individuals) develop paralytic polio.
The acute flaccid weakness ranges from one muscle or group of muscles to quadriplegia and respiratory failure. Proximal muscles usually are affected more than distal muscles, and legs more commonly than arms. Reflexes are decreased or absent.
•Diagnosis – The diagnosis of poliomyelitis should be suspected in patients with aseptic meningitis and acute flaccid weakness. In addition, suspicion should be increased for symptomatic patients in the setting of epidemiologic exposure, particularly among unvaccinated individuals. The diagnosis of poliomyelitis is established by identifying the virus from stool samples, oropharyngeal swabs, and/or cerebrospinal fluid. (See 'Diagnosis' above.)
•Differential diagnosis – The differential diagnosis of poliomyelitis includes other infectious and noninfectious causes of acute flaccid paralysis (table 2). The conditions that most resemble acute flaccid paralysis from poliomyelitis include other infectious causes of acute flaccid paralysis (non-polio enteroviruses or West Nile virus) and Guillain-Barré syndrome (GBS). (See 'Differential diagnosis' above.)
•Management – Treatment of poliomyelitis is supportive. Respiratory failure may develop, requiring mechanical ventilation. Patients with bulbar involvement require close monitoring of cardiovascular status because of the association with blood pressure fluctuations, circulatory collapse, and autonomic dysfunction. (See 'Management' above.)
●Post-polio syndrome
•Definition – Post-polio syndrome (PPS) is characterized by new or progressive muscle weakness with functional deterioration after a prolonged period of stability in patients with a history of acute flaccid paralysis from polio. The cause of progressive neurologic deterioration in patients with PPS is unknown. (See 'Epidemiology' above and 'Pathogenesis' above.)
•Clinical features – Symptoms of PPS include progressive muscle weakness, fatigue, and pain in the muscles or joints. (See 'Clinical manifestations' above.)
•Diagnosis – The clinical diagnosis of PPS is made in patients with a remote history of poliomyelitis who develop new, progressive muscle weakness after diagnostic testing has excluded alternative conditions. (See 'Diagnosis' above and 'Differential diagnosis' above.)
•Management – The management of PPS consists of symptomatic care. For patients with PPS who are able to participate, we suggest treatment with a nonfatiguing exercise program. Energy conservation techniques such as the pacing of physical activities may be help treat generalized fatigue. (See 'Management' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Burk Jubelt, MD, who contributed to earlier versions of this topic review.
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