Acute Poliomyelitis 

Updated: Jun 22, 2018
Author: Christine L Munson, MD; Chief Editor: Stephen Kishner, MD, MHA 



Acute poliomyelitis is a disease of the anterior horn motor neurons of the spinal cord and brain stem caused by poliovirus. Flaccid asymmetric weakness and muscle atrophy are the hallmarks of its clinical manifestations, due to loss of motor neurons and denervation of their associated skeletal muscles. Because of the success of poliovirus vaccine, poliomyelitis, once one of the most feared human infectious diseases, is now almost entirely preventable by proper immunization (see image below).

The typical contractures of postpolio residual par The typical contractures of postpolio residual paralysis.

See Pediatric Vaccinations: Do You Know the Recommended Schedules?, a Critical Images slideshow, to help stay current with the latest routine and catch-up immunization schedules for 16 vaccine-preventable diseases.

In 1988, the World Health Organization initiated the Global Polio Eradication Initiative to eradicate poliomyelitis; at the time, it was endemic in 125 countries. By 2016, only three countries, Pakistan, Afghanistan, and Nigeria, were endemic for polio;[1] however, the campaign to eradicate polio continues today, as do efforts to prevent transmission of the disease into polio-free areas.[2, 3, 4, 5, 6]


Acute poliomyelitis is caused by small ribonucleic acid (RNA) viruses of the enterovirus group of the picornavirus family. The single-stranded RNA core is surrounded by a protein capsid without a lipid envelope, which makes poliovirus resistant to lipid solvents and stable at low pH. Three antigenically distinct strains are known, with type I accounting for 85% of cases of paralytic illnesses. Infection with one type does not protect from the other types; however, immunity to each of the 3 strains is lifelong.

The enteroviruses of poliomyelitis infect the human intestinal tract mainly through the fecal-oral route (hand to mouth). The viruses multiply in oropharyngeal and lower gastrointestinal tract mucosa during the first 1-3 weeks of the incubation period. Virus may be secreted in saliva and feces during this period, causing most host-to-host transmission. After the initial alimentary phase, the virus drains into the cervical and mesenteric lymph nodes and then into the blood stream. Only 5% of infected patients have selective nervous system involvement after viremia. It is believed that replication in extraneural sites maintains the viremia and increases the likelihood that the virus will enter the nervous system.

The poliovirus enters the nervous system by either crossing the blood-brain barrier or by axonal transportation from a peripheral nerve. It can cause nervous system infection by involving the precentral gyrus, thalamus, hypothalamus, motor nuclei of the brainstem and surrounding reticular formation, vestibular and cerebellar nuclei, and neurons of the anterior and intermediate columns of the spinal cord. The nerve cells undergo central chromatolysis along with an inflammatory reaction while multiplication of the virus precedes onset of paralysis. As the chromatolysis process goes on further, muscle paralysis or even atrophy appears when fewer than 10% of neurons survive in the corresponding cord segments. Gliosis develops when the inflammatory infiltrate has subsided, but most surviving neurons show full recovery.[7, 8]



United States

Because of widespread use of the poliovirus vaccine, the incidence rate has been less than 0.01 cases per 100,000 population since 1965. The last case of wild-type polio in the United States was in 1979. Only a few cases of paralytic poliomyelitis are reported each year in the United States. Vaccine-derived poliovirus infections are seen primarily in low-vaccination communities. Rare cases of poliomyelitis are reported due to live attenuated poliovirus vaccine. Small pockets of poliomyelitis epidemics still exist among isolated religious sects, such as the Amish. These groups usually choose not to participate in government-sponsored public health services, such as immunizations for infectious diseases.


Acute poliomyelitis has had a worldwide distribution, with a peak season from July to September and a concentration in tropical areas of the Northern Hemisphere. The condition continues to occur epidemically in nonimmunized populations in developing regions. Poor sanitation and crowded circumstances are two additional factors associated with dissemination. Internationally, importation of polio continues to occur into polio-free countries. From 2002-2005, 21 previously polio-free countries experienced a resurgence of wild-type polio.[9] In eight of those countries, the cases were limited and no further spread was observed. In the remaining 13 countries, multiple cases were observed, with the outbreak lasting less than 6 months.[10, 11] In October 2013, Syria reported that, after having been eradicated there 15 years earlier, polio had returned to that country, with 13 cases from the Deir Al Zour province, caused by wild poliovirus type I, having been confirmed.[12]

As of 2018, wild-type polio remained endemic in Pakistan and Afghanistan; by late April, cases for 2018 numbered one in Pakistan and seven in Afghanistan. In 2016, it was discovered that wild poliovirus transmission was also endemic in Nigeria, although the virus was not detected there in 2017 or, as of a May report by the Centers for Disease Control and Prevention (CDC), in 2018. (However, the CDC report stated that because of access limitations for poliovirus surveillance in insurgent-held areas of Nigeria, the virus could have continued to be transmitted in that country undetected.)[1]


Of acute poliovirus infections, 4-8% show only nonspecific illness, and 1-2% of infections finally result in neurologic symptoms. The incidence of paralytic diseases increases with young age, advanced age, recent hard exercise, tonsillectomy, pregnancy, and impairment of B-lymphocyte defenses. The mortality from acute paralytic poliomyelitis is 5-10%, but it can reach 20-60% in cases of bulbar involvement.


Acute poliomyelitis has no racial predilection.


The male-to-female ratio for acute poliomyelitis is 1:1.


Most cases of acute poliomyelitis occur in the pediatric population. Infection or immunization against poliovirus provides lifelong protection.




Most patients (95%) with poliomyelitis virus infections are asymptomatic or have only mild systemic symptoms, such as pharyngitis or gastroenteritis. These cases are referred to as minor illness or abortive poliomyelitis. The mild symptoms are related to viremia and immune response against dissemination of the virus. Only 5% of patients exhibit different severities of nervous system involvement, from nonparalytic poliomyelitis to the most severe form of paralytic poliomyelitis.[7]

  • Nonparalytic poliomyelitis or preparalytic poliomyelitis

    • The prodromal symptoms include generalized, nonthrobbing headache; fever of 38-40 º C; sore throat; anorexia; nausea; vomiting; and muscle aches. These symptoms may or may not subside in 1-2 weeks.

    • Headache and fever, as well as signs and symptoms of nervous system involvement (eg, irritability, restlessness, apprehensiveness, emotional instability, stiffness of the neck and back) and Kernig and Brudzinski signs because of meningitis, then may follow.

    • Children generally exhibit milder systemic symptoms than do adults.

    • Preparalytic symptoms also may develop into paralytic ones.

  • Paralytic poliomyelitis

    • The incubation period from virus exposure to the neurologic phase can last 4-10 days but may extend to 4-5 weeks.

    • Severe muscle pain and spasms, followed by weakness, develop. Muscle weakness tends to become maximal within 48 hours but may develop for longer than a week. No progression of weakness should be noted after the temperature drops to normal for 48 hours. Weakness is asymmetric, with the lower limbs affected more than upper limbs.

    • Muscle tone is flaccid, and the reflexes initially are brisk but then become absent. The transient or occasionally persistent coarse fasciculations also are observed frequently in patients with paralytic poliomyelitis.

    • Patients also complain of paresthesias in the affected limbs without real sensation loss.

    • Paralysis remains for days or weeks before slow recovery occurs over months or years. Which factors favor development of paralytic disease remains unclear, but some evidence exists that physical activity and intramuscular injections during the prodrome may be important exacerbating factors.[7]

  • Paralytic poliomyelitis with bulbar involvement

    • The purely bulbar form of poliomyelitis without limb weakness may occur in children, particularly in those whose tonsils and adenoids have been removed.

    • Bulbar paralysis with spinal involvement is more common in adults, most frequently involving the medulla and leading to dysphagia, dysphonia, respiratory failure, and vasomotor disturbance.

    • Patients may have symptoms and signs, such as hiccough, shallowness and slowing of respiration, cyanosis, restlessness, and anxiety.

    • When paralysis of diaphragmatic and intercostal musculature also occurs, patients need immediate respiratory assistance and intensive care because of life-threatening respiratory failure. Cranial nerve and bulbar involvement can cause obstruction, due to decreased respiratory drive and associated problems with mucus plugging or actual pharyngeal weakness-induced direct airway obstruction. The loss of vasomotor control with circulatory collapse also contributes to high mortality.

    • The encephalitic form of poliomyelitis

      • This form is very rare and manifests as agitation, confusion, stupor, and coma.

      • Autonomic dysfunction is common, and it has a high mortality.


Vital signs are the key to monitoring patients with poliovirus infection.

  • Muscle weakness can be assessed by muscle strength testing.

    • Usually asymmetric proximal weakness is present with more involvement of lumbar than cervical segments and more spinal cord than brainstem segments.

    • The trunk muscles are affected least.

    • Sensation should be within normal limits objectively.

    • Deep tendon reflexes are diminished or absent.

    • Atrophy of muscle may be detected 3 weeks after onset of paralysis, which becomes maximal at 12-15 weeks and remains permanent.

  • Fifty percent of adult patients with poliomyelitis experience transient acute urinary retention.

  • Stiffness and pain in the neck and back because of meningeal irritation, as well as abnormalities of autonomic function, also can be seen in some patients.

  • Cranial nerve involvement

    • Approximately 10-15% of cases affect the lower brainstem motor nuclei.

    • When the ninth and tenth cranial nerve nuclei are involved, patients develop paralysis of pharyngeal and laryngeal musculature. Unilateral or bilateral facial muscles, as well as the tongue and mastication muscles, may become paralyzed.

    • External oculomotor weakness with pupil sparing may occur in rare cases.

    • Direct infection of the brainstem reticular formation can cause breathing and swallowing disruption, as well as loss of control of the cardiovascular system.


The carrier with poliomyelitis virus infection is one major source of virus spread from person to person. The major route is oral-fecal transmission. The greatest dissemination of virus occurs within families with poor sanitation and hygiene or crowded circumstances.



Diagnostic Considerations

These include the following:

  • Acute meningitides

  • Other motor polyneuropathies

  • Acute intermittent porphyria

  • Acute transverse myelitis

  • Acute encephalitides caused by coxsackievirus and echoviruses

  • Other enteroviruses (Coxsackie)

  • Flaviviruses (Japanese encephalitis, West Nile)

  • HIV neuropathy

  • Diphtheria

  • Borrelia burgdorferi infection

  • Botulism

Differential Diagnoses



Laboratory Studies

See the list below:

  • Order lumbar puncture test.

    • Cerebrospinal fluid (CSF) pressure may be increased.

    • Pleocytosis (neutrophils in the first few days, then lymphocytes) may be noted in the CSF during the period before onset of paralysis in acute poliomyelitis.

    • The CSF protein content may be elevated slightly with a normal glucose, except in patients with severe paralysis, who may demonstrate protein elevations to 100-300 mg/dL for several weeks.

  • Order a complete blood count (CBC), because leukocytosis may be present.

  • Perform virus recovery from throat washing, stool culture, blood culture, and CSF culture. Viral studies in stool specimens are essential for the diagnosis of poliomyelitis.

    • Recover virus from throat washing during the first week and stool culture from the first 2-5 weeks.

    • In rare cases, the virus may be isolated from CSF or serum, in contrast to the paralytic illnesses caused by other enteroviruses.

    • These tests require additional demonstration of a 4-fold rise in the virus antibody titer to make a specific diagnosis.

  • Polymerase chain reaction is routinely used to differentiate wild-type strains from vaccine strains.

Imaging Studies

See the list below:

  • Magnetic resonance imaging (MRI) may show localization of inflammation to the spinal cord anterior horns.


See the list below:

  • Electromyography

    • The earliest electromyographic finding in poliomyelitis is a reduction in the recruitment pattern and a diminished interference pattern due to acute motor axon fiber involvement.

    • Fibrillations develop in 2-4 weeks and persist indefinitely; fasciculations also may be observed.

    • Motor unit action potentials initially have decreased amplitude and then become large in amplitude with increased duration. Later, polyphasic motor units are observed because of nerve reinnervation.

    • The motor nerve conduction velocities remain within normal limits; however, the compound muscle action potential (CMAP) is reduced in direct proportion to the number of motor axons that are affected. Sensory nerve conduction studies remain within normal parameters, due to sparing of the dorsal root ganglion.

Histologic Findings

Under microscopy, the spinal anterior horn cells are surrounded by inflammatory cells. Spongiosis of the gray matter, containing many scattered inflammatory cells, also is noted. Most inflammatory cells are neutrophil leukocytes.

Other Tests

A study by Brehm et al indicated that in polio survivors, the 6-minute walk test (6MWT) and the 6-minute walking energy cost test (WECT) are dependable means of evaluating walking capacity, with the test-retest reliability of both considered excellent. The tests are not interchangeable, however; the study recommended that the 6MWT be used to assess maximal walking capacity and the WECT be employed to measure submaximal walking capacity. The investigators also reported that the sensitivity of the 6MWT in detecting change for walked distance is slightly greater than that of the WECT.[13]



Rehabilitation Program

Physical Therapy

Physical therapy plays an important role in rehabilitation for patients with poliomyelitis. Patients with muscle paralysis benefit from frequent passive range of motion (PROM) and splinting of joints to prevent contracture and joint ankylosis. Chest physical therapy (CPT) helps patients with bulbar involvement prevent any pulmonary complications, such as atelectasis. Frequent repositioning of paralyzed patients helps to prevent bedsores (see image below).

Orthotic treatment for deformities around the knee Orthotic treatment for deformities around the knee in poliomyelitis.

Occupational Therapy

Patients with paralysis of the extremities may benefit from hand or arm splints, knee or trochanter rolls, a footboard, or Multi-Podus boots to prevent foot drop, ulcers, and other deformities. Hot packs also are helpful to relieve the muscle pain.

Speech Therapy

Patients with cranial nerve involvement may develop swallowing dysfunction. To protect the airway and prevent aspiration pneumonia, a speech therapist needs to be involved early to perform an evaluation of the safety of swallowing. Decisions on the appropriate consistency of oral foods and use of various strategies/techniques greatly reduce the risk of aspiration. Periodic follow up of patient status can be performed with serial video swallow testing.

Recreational Therapy

Patients may attend leisure activities to reduce stress and learn how to get involved in group activities.

Medical Issues/Complications

All patients should be placed on bedrest in an isolation unit. Monitor patients' vital signs carefully; focus especially on the swallowing function, vital capacity, pulse, and blood pressure, in anticipation of respiratory or circulatory complications. Patients who develop respiratory failure because of depression of the brainstem respiratory center, in addition to paralysis of the intercostal and diaphragmatic muscles, may require immediate positive pressure ventilation and/or tracheotomy in the respiratory intensive care unit.

Surgical Intervention

In severe cases of contracture from limb immobilization, the patient may benefit from orthopedic surgery to release the contracture and restore limb function (see image below).

Surgical correction of a fixed flexion deformity o Surgical correction of a fixed flexion deformity of the knee and hip due to iliotibial band contracture, by Souttar and Yount's release.

Other Treatment

No specific treatment exists for acute poliomyelitis except supportive care, which may help to ensure survival, modify the disability, and improve the outcome.



Medication Summary

Prevention has been proven to be the key to treatment for poliomyelitis. Development of effective vaccines from cultures of human embryonic tissues and monkey kidney cells represent significant achievements. As a result of the introduction of inactivated poliovirus vaccine in the 1950s, followed by oral poliovirus vaccine in the 1960s, cases of poliomyelitis in the United States have become rare following vaccination. Inadequate use of the vaccine in areas with low standards for public health still may increase the risk of outbreaks of poliomyelitis because of lack of immunity.


Class Summary

Provide active immunity against poliovirus

Salk vaccine (inactivated poliovirus vaccine [IPV])

Two IPV products are licensed in the United States, although only 1 of these (IPOL) is distributed there. IPV contains formalin-inactivated poliovirus strains of the 3 different serotypes (Mahoney, MEF-1, Saukett). Administered through injection, stimulates serum IgM, IgG, and IgA. Data have confirmed that 90-100% of children develop protective antibodies to all 3 types of poliovirus after administration of 2 doses of currently available IPV, and 99-100% develop protective antibodies after 3 doses. The current recommended polio vaccination schedule in children is 4 doses of the IPV with one dose at each of the following ages: 2 months, 4 months, between 6 to 18 months, and a booster between 4 to 6 years of age. Routine poliovirus vaccination of adults residing in the United States is not necessary.

High-risk adults (eg, travelers to epidemic areas, members of community with poliovirus disease, health care workers with close contact of patients who might excrete wild poliovirus, unvaccinated adults whose children will receive oral polio vaccine) should be vaccinated.

IPV is the only vaccine recommended for vaccination of immunodeficient persons and their household contacts.

Sabin vaccine (Orimune)

Consists of attenuated live poliovirus. Sabin vaccine is very effective in providing local gastrointestinal immunity and circulating antibodies.

Routine immunization using oral polio vaccine (OPV) in the United States has been discontinued to eliminate the risk for vaccine-associated paralytic poliomyelitis (VAPP) according to the 2000 ACIP new recommendations. However, an emergency stockpile of OPV for polio outbreak control is maintained.



Further Outpatient Care

See the list below:

  • Continue physical therapy on an outpatient basis to help muscle reeducation. Specific exercise programs for strengthening lower extremities are helpful to avoid contracture and muscle atrophy. Individuals with bowel and bladder problems need ongoing follow-up as outpatients.


See the list below:

  • Poliovirus vaccines have been recommended for all pediatric populations in the United States. Vaccination is the most powerful means of prevention, and it has helped to bring about dramatic reduction in the incidence of poliomyelitis. The Western Hemisphere was certified as free of indigenous wild poliovirus in 1994. The recommendation for routine childhood poliovirus vaccination has been changed from an all-OPV schedule to a sequential IPV-OPV vaccination schedule. As of January 1, 2000, the ACIP has recommended exclusive use of IPV for routine childhood polio vaccination in the United States based on the continued occurrence of VAPP, the absence of indigenous disease, and the sharply decreased risk for wild poliovirus importation into the United States (see Medication).


See the list below:

  • Urinary tract infection usually is transient during acute phase poliomyelitis. Other complications (eg, atelectasis, pneumonia, pulmonary edema, myocarditis) also may occur. Respiratory failure may be the result of respiratory muscle paralysis or airway obstruction from lesions of the cranial nerve nuclei or respiratory center. Related problems caused by central and spinal loss of respiratory drive with mucus plugging or actual pharyngeal weakness may induce direct airway obstruction.


The overall prognosis for patients with poliomyelitis is good. Only 5-10% mortality (slightly higher in pediatric and elderly populations) results from acute paralytic poliomyelitis because of respiratory and cardiovascular impairments. Most patients recover from respiratory failure, and only a small percentage of patients need chronic respirator care. Muscle strength from paralyzed muscles may achieve approximately 60% recovery in the first 3-4 months, probably because of reinnervation of the denervated muscle fibers. Slow recovery may continue for about a year because of hypertrophy of the undamaged muscle.

Postpolio syndrome

The diagnosis of postpolio syndrome (PPS) can be made when a new history of decreased muscle strength, weakness, and atrophy in an asymmetric distribution compatible with previous polio is noted, along with electrophysiologic features of acute denervation superimposed on chronic denervation-reinnervation in the absence of another neuromuscular cause.

Slow but gradual progressive weakness occurs decades after the acute attack of poliomyelitis. The weakness could develop in already affected muscles or muscles previously thought to be unaffected. The new symptoms often are accompanied by fasciculations or additional atrophy. Patients also may report fatigue, muscle and joint pain, and intolerance to cold.

PPS is not infectious in origin; rather, it is associated with increasing dysfunction in surviving motor neurons, which has been demonstrated through muscle biopsy showing active denervation and reinnervation. The overall prognosis is good with slow progression of weakness, rarely causing further disability or death.

The etiology of PPS is unclear. A number of possible mechanisms have been suggested to account for the condition. The development of PPS depends on the severity of the acute illness rather than on the age of the patient. Immunologic mechanisms also are suggested, because of the presence of mild inflammatory changes in muscle biopsy. PPS may primarily be caused by a process of attrition and premature neuronal exhaustion. The dysfunction of the muscles results from the loss of motor neurons and reduced neuromuscular reserve capacity, in combination with a disturbed balance between the ongoing reinnervation and denervation, at the expense of reinnervation.

Orthopedic complications result from prolonged, abnormal stresses from skeletal deformity and muscle weakness. These complications include osteoporosis, fractures, instability of joints, osteoarthritis, and scoliosis.

Neurologic complications tend to result from skeletal deformity and the subsequent lifelong use of adaptive equipment. Peripheral nerve entrapments are common with the use of crutches, wheelchairs, and other adaptive devices.[14]

Key to the treatment of PPS, other than the active involvement of multidisciplinary rehabilitation team members, is energy conservation. Patients should brace their weak muscles, perform only nonfatiguing exercises, simplify their work duties, learn effective time management, take adequate rest breaks, and correlate activity with their symptoms. Modification of their diet and sleep patterns is also essential to improve function.

A prospective, randomized, controlled study from Turkey looked at the effects of home- and hospital-based exercise programs on functional capacity, fatigue, and quality of life in patients with PPS.[15] The results indicated that such programs, whether carried out at home or in a hospital, can improve fatigue problems and quality of life in these patients. The study's hospital exercise group also demonstrated improvement in functional capacity.

In a study of 16 polio survivors with weakened calf muscles, Ploeger et al found evidence that dorsiflexion-restricting ankle-foot orthoses (DR-AFOs) can reduce walking difficulties. Using three-dimensional gait analysis to evaluate gait biomechanics, as well as a 6MWT to assess comfortable gait speed and walking energy cost (from ambulant registration of gas exchange), the study compared results between walking with the use of DR-AFOs and walking in shoes only. In addition, questionnaires were used to determine patients’ perceived walking ability. The study indicated that DR-AFO use resulted in better gait biomechanics, gait speed, and perception of walking ability, while reducing walking energy cost. The results also suggested, however, that the efficacy of the orthoses varied according to patients’ shoes-only gait pattern.[16]

Patient Education

See the list below:

  • As poliomyelitis became a rare disease following the development of the poliovirus vaccine, postpolio syndrome (PPS) began to attract more attention. Public education on the importance of mass vaccination programs for poliovirus — not only in the United States, but also around the world — is helping to eradicate this debilitating paralytic illness.

  • Education on PPS, especially among individuals with a history of poliomyelitis, helps patients understand their own disease and contribute to its management. Patients may find additional information regarding PPS from organizations such as Post-Polio Health International, 4207 Lindel Blvd #110, St. Louis, MO 63108-2915 USA, telephone (314) 534-0475. Another organization that may be helpful is WWW.POSTPOLIO.ORG.

  • For patient education resources, see the Children's Health Center and Brain and Nervous System Center. Also, see Immunization Schedule, Children and Brain Infection.