Pediatrics

Polio

OVERVIEW: What every practitioner needs to know

Are you sure your patient has poliomyelitis? What are the typical findings for this disease?

Poliomyelitis is an acute highly contagious infection caused by polioviruses, a positive stranded RNA virus from the genus Enterovirus. Polioviruses are able to remain in the soil and water for weeks, and they have a high recombination capacity. Infections with poliviruses are frequently asymptomatic but may cause illness ranging from mild fever to acute flaccid paralysis or aseptic meningitis in 1-2% of cases.

Poliomyelitis should be suspected in any child or adolescent presenting with fever, headache, muscle aches and acute onset weakness. Diagnosis of poliomyeltiis is confirmed from isolation of polioviruses from the stool, cerebrospinal fluid or throat viral culture or PCR. Treatment is aimed at reducing complications from poliomyelitis and alleviating symptoms. Appropriate vaccination against poliomyelitis with IPV is crucial to prevent the disease, even in non endemic countries.

Typical findings:

Poliomyelitis should be suspected in any child or adolescent who presents with acute onset of weakness or paralysis, in whom fever, headache and vomiting may have preceded for 1 to 3 days.

Poliomyelitis in its most severe and classical form presents as acute flaccid paralysis in 1% of the infections. It is characterized by rapid onset of asymmetric weakness, fever, headaches and muscle pains. Morefrequent but likely unrecognized presentations include minor malaise(asymptomatic or subclinical infections in 90%); minor illnesspresenting as fever with drowsiness, headache and vomiting in 8% ofinfections; and aseptic meningitis in 1-2% of infections.

Since 1991, no cases of wild type poliomyelitis have been reported inthe region of the Americas including the United States, and globallythere has been a 99% reduction in the number of cases of poliomyelitissince 1988. However, the use ofthe oral polio vaccine (Sabin viruses) has been a cause of vaccineassociated paralytic polio (VAPP), and vaccine-derived poliovirus (VDPV)paralysis. Both areindistinguishable from acute wild poliomyelitis, and are due to thereversion of the live attenuated vaccine virus into a more neurovirulentvirus.

How to approach the diagnosis of a child or adolescent with unilateral or bilateral acute weakness?

Acute onset of weakness in a child or adolescent is an emergency. The clinical finding that must be established to determine the correct diagnosis is the location of the lesion. Differentiation between a central (upper motor neuron), and peripheral (lower motor neuron) lesion is the first step in determining the extent of the disease. Associated CNS abnormalities including seizures, headaches, encephalopathy, hyperreflexia, hypertonia, and meningeal signs are all consistent with cortical (brain or spinal) involvement. Preserved level of cognition, hyporeflexia, hypotonia, sensory level weakness and loss of sphincter reflexes (urethral or anal) are more consistent with peripheral nervous system disease.

Is the acute weakness unilateral or bilateral?

Poliomyelitis usually presents as unilateral weakness, but it may also be bilateral. Asymmetric weakness helps differentiate poliomyelitis from other causes of acute flaccid weakness or paralysis. Unilateral weakness is suggestive of peripheral nerve or nerve root involvement, including neuropathy, plexopathy, radiculopathy and facial palsy (Bell´s palsy). Bilateral weakness is more commonly due to acute inflammatory polyradiculoneuropathy (Guillain-Barre syndrome or GBS) characterized by ascending symmetric weakness.

Miller Fisher GBS variant is defined as facial palsy with opthalmoplegia. Myasthenia gravis and botulism can present with bilateral or generalized weakness due to neuromuscular junction disruption. Affected children commonly have cranial nerve involvement and intermittent course. Acute myopathic disease can mimic bilateral weakness, but reflexes are usually preserved.

What other disease/condition shares some of these symptoms?

In the countries of the Americas, including the United States, there have been no cases of acute poliomyelitis due to wild poliovirus since 1991. However, cases of vaccine-associated (VAPP) and vaccine-derived (VDPV) acute poliomyelitis continue to occur throughout the continent in areas where oral polio vaccine is in use for routine immunization. Children presenting with VAPP or VDPV are indistinguishable from wild poliovirus cases.

Other enteroviruses, like EV71 also may manifest as acute flaccid paralysis, especially in Asia. West Nile virus in children could also mimic acute poliomyelitis. The most common cause of acute weakness in polio free or non-endemic countries is Guillain-Barre syndrome (GBS), which presents with a frequency of 1 to 3 cases per 100,000 children less than 15 years of age and is usually an ascending symmetric paralysis. Other infections which should be considered in children and adolescents with acute paralysis include: rabies, varicella-zoster, Japanese encephalitis, acute transverse myelitis, epidural abscess and tick bite paralysis.

What caused this disease to develop at this time?

The most important factor predisposing to poliomyelitis is not being fully immunized with one of the two available vaccines - IPV in most higher and middle income countries, or OPV in lower and middle income countries.

Exposure to travelers from polio endemic areas is also a risk factor.

Intramuscular injections given to children who have acquired an infection with poliovirus has been linked to a higher risk of developing paralysis (provocation paralysis) in low and middle income countries.

Tonsillectomy has also been linked to a higher manifestation of bulbar poliomyelitis.

Studies from Norway have shown that the Fc gamma RIIIA V/V genotype may lower the risk for contracting acute poliomyelitis through better clearance of poliovirus.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Initial laboratories should include a complete blood count, cerebrospinal fluid sample, and EMG studies. Cerebrospinal fluid will show increased leukocytes between 10 to 200 wbc/mm3 (rarely more than 500 wbc/mm3). Elevated protein is common averaging 40-50 mg/dL. CSF glucose is seldom abnormal.

To confirm the diagnosis, the World Health Organization (WHO) and the Centers for Disease Control (CDC) recommend isolation of poliovirus from the stool, oropharyinx or cerebrospinal fluid as soon as possible after initiation of the acute flaccid paralysis. Two stool samples 24-48 hours apart are preferable for recovery of the virus. Virus persists in the oropharynx for 1 week, and in the stool up to 6 to 8 weeks after onset. Recovery of the virus falls from 80% the first 2 weeks to 25% at 5 to 6 weeks. Children with humoral immunodeficiency can excrete the virus for long periods, up to many years.

Serologic testing against polioviruses can demonstrate seroconversion (four fold or greater increase in neutralization titers) 3 to 6 weeks after the acute onset of illness. Serologic testing could be difficult to interpret in previously vaccinated but unprotected children and adolescents.

Would imaging studies be helpful? If so, which ones?

Magnetic Resonance Imaging (MRI) could be helpful to exclude other causes of acute flaccid paralysis. In some reports, an increased signal intensity involving ventral horn cells of the spinal cord has been reported on T2-weighted images with and without contrast enhancement. MRI cannot differentiate poliomyelitis from other acute demyelinating diseases like ADEM or AMAN.

Confirming the diagnosis

See Figure 1.

Figure 1.

If you are able to confirm that the patient has poliomyelitis, what treatment should be initiated?

Antiviral drugs for the treatment of poliomyelitis are not available. Management is supportive and directed at relieving symptoms and complications.

In the acute phase of paralytic poliomyelitis patients should be hospitalized:

- Bed rest may prevent worsening of the paralysis.

- Hot moist packs are helpful at relieving muscle pain and spasms.

- Monitoring of respiratory vital capacity is imperative. If paralysis of respiratory muscles results in a fall in vital capacity below 50%, mechanical ventilation to avoid hypoxia should be instituted.

- Avoid unnecessary intramuscular injections.

- Urinary bladder paralysis may require intermittent catheterization.

Physical therapy should be initiated once the progression of paralysis has ceased, usually 1 week after onset.

What are the adverse effects associated with each treatment option?

N/A

What are the possible outcomes of poliomyelitis?

Muscular paralysis usually progresses or extends for only 1 to 3 days after its onset, but occasionally for as long as 1 week. Permanent weakness is observed in approximately two thirds of patients with paralytic poliomyelitis. Complete recovery is less likely when acute paralysis is severe and when patients require mechanical ventilation. An estimate of the eventual outcome can be made after 1 month, when most reversible damage has disappeared. Very little additional return of function can be expected beyond 9 months. Recovery from pharyngeal paralysis usually is evident by 10 days and is eventually complete. Bulbar poliomyelitis is rarely responsible for permanent sequelae in surviving patients.

Available mortality figures date from the era of epidemic poliomyelitis, a period when critical care medicine was less advanced than it is today. The reported overall mortality for acute paralytic poliomyelitis during this period was 5% to 10%, but was substantially higher with bulbar involvement.

What causes this disease and how frequent is it?

Polioviruses are members of the enteroviruses, also known as “summer viruses”. There are three serotypes of poliovirus and before successful vaccines were available virtually all children were infected by adolescence or young adulthood. As hygienic conditions improved in North America, more young adults became infected and paralyzed at older ages.

Only four countries in the world remain endemic for wild polioviruses (India, Afghanistan, Pakistan and Nigeria). Importations from these countries to neighboring areas in Asia, Africa, Europe and North America have been reported.

Poliomyelitis is a ubiquitous, highly contagious, seasonal disease presenting during the rainy season or summer months.

Wild polioviruses are readily transmitted person-to-person through fecal–oral and oral–oral routes; less frequently by a common vehicle like water or milk. Vaccine derived polioviruses can circulate in communities with low vaccine coverage for years before becoming detected or causing paralytic cases. High population immunity and vaccine herd protection are critical to avoid reintroduction of polioviruses in disease free countries.

How do these pathogens/genes/exposures cause the disease?

Polioviruses enter the oral mucosa and replicate in the gut and adjacent lymphoid tissues, they then disseminate to susceptible reticuloendothelial tissues via a minor viremia. In a few infected persons, replication in the reticuloendothelial system gives rise to a major viremia, which corresponds with the minor illness and causes the symptoms associated with abortive poliomyelitis.

In the most severe cases, polioviruses infect neurons in the gray matter of the brain and spinal cord using retrograde axonal invasion. Poliovirus principally affects motor and autonomic neurons. Neuronal destruction is accompanied by inflammatory lesions consisting of polymorphonuclear leukocytes, lymphocytes, and macrophages that are distributed throughout the gray matter of the anterior horns of the spinal cord and the motor nuclei of the pons and medulla.

Clinical symptoms depend on the severity of lesions rather than on their distribution, which is similar in essentially all cases; almost all fatal cases have involvement of both the spinal cord and cranial nerve nuclei and brain stem, even in the absence of bulbar signs. The dorsal root ganglia are commonly involved pathologically, but this does not result in sensory deficits. Polioviruses can be isolated from the spinal cord for only the first few days after the onset of paralysis, but the inflammatory lesions may persist for months.

Other clinical manifestations that might help with diagnosis and management

None.

What complications might you expect from the disease or treatment of the disease?

Permanent paralysis occurs in 1% of poliovirus infections and it was higher in older children and adolescents. In children younger than 3 years of age only 19% had paralysis of both arms and legs, while in patients older than 25 years 55% of became quadriplegic. Mortality from poliomyelitis also increases with age from 5% in younger children to 23.5% in adults older than 25 years.

Post-polio syndrome (PPS), described in the early 1980s, refers to a disease entity that encompasses the late manifestations of paralytic poliomyelitis. After an interval of 15 to 40 years, 25 to 40% of the patients who contracted paralytic poliomyelitis in their childhood may develop muscle pain and exacerbation of existing weakness or new weakness or paralysis. Factors that enhance the risk of PPS include female gender, multiple injections and time since acute paralysis. PPS is not a consequence of persistent infection. The pathogenesis of PPS probably involves late attrition of oversized motor units during the recovery process of paralytic poliomyelitis.

Are additional laboratory studies available; even some that are not widely available?

Detection of polioviruses by polymerase chain reaction (PCR) is now possible from CSF, stool and pharyngeal samples and specimens. This test is only performed at the refererence laboratories of the CDC and WHO.

How can poliomyelitis be prevented?

Vaccination is the only known method for preventing poliomyelitis. There are two very effective vaccines available for the prevention of poliomyelitis. The inactivated polio vaccine (IPV) developed by Jonas Salk in 1955, was the first vaccine available and was successful at reducing poliomyelitis outbreaks in the United States and other countries. The oral polio vaccine (OPV), a live attenuated vaccine developed later by Albert Sabin, has been the cornerstone of the polio eradication program around the world.

The OPV vaccine is associated with the rare occurrence of VAPP, which can present after 1 of every 750,000 to 2.6 million doses of vaccine. It is estimated that 250-500 cases of VAPP continue to occur each year in countries using OPV. OPV derived vaccine viruses (VDPV) can circulate in communities with vaccine coverage below 90% and revert to neurovirulent viruses. At least 20 outbreaks in 18 countries have been described so far and they can persist for several years unless the population immunity to polio is improved through vaccination.

Both vaccines are given in a 4 dose schedule, with a 3 dose primary series in the first year of life and a booster dose in the preschool years. Since 2000 IPV has been the only recommended polio vaccine in the United States because of concern about the risk of VAPP or VDPV.

What is the evidence?

Marx, A, Glass, JD, Sutter, RW. "Differential diagnosis of acute flaccid paralysis and its role in poliomyelitis surveillance". Epidemiologic Reviews. vol. 22. 2000. pp. 298.

Melnick, JL. "Current status of poliovirus infections". Clinical Microbiol Reviews.. vol. 9. 1996. pp. 293-300.

Nathanson, N, Kew, OM. "From Emergence to eradication: the epidemiology of poliomyelitis deconstructed". Am J Epidemiol. vol. 172. 2010. pp. 1213-1229.

Ongoing controversies regarding etiology, diagnosis, treatment

During 2000 and 2001, an outbreak of 21 cases of paralytic poliomyelitis on the island of Hispaniola occurred, caused by a virulent strain genetically related to the type 1 Sabin OPV vaccine strain. Since then, other outbreaks of paralytic disease caused by vaccine-derived polioviruses (VDPVs) have been discovered in underimmunized children living in economically deprived regions. The low immunization rates in these areas have permitted these viruses to circulate for long periods and, by continuous mutation, acquire biologic properties indistinguishable from those of naturally occurring wild polioviruses.

The emergence of VDPV has profoundly influenced plans for the eventual cessation of poliovirus immunization following eradication of poliomyelitis, which will now include a strategy to discontinue OPV use worldwide, introduce IPV into as many countries as feasible, and develop an OPV vaccine stockpile for use anywhere in the world, and a plan for containment of laboratory stocks of naturally occurring and attenuated polioviruses.

You must be a registered member of Clinical Pain Advisor to post a comment.

Sign Up for Free e-Newsletters