POLIOMYELITIS

POLIOMYELITIS

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.

In 1988, the World Health Organization initiated the Global Polio Eradication Initiative to eradicate poliomyelitis; at the time, it was endemic in 125 countries. 

As of 2006, only 6 countries were endemic for polio; however, the worldwide campaign to eradicate polio continues today, as do efforts to prevent transmission of the disease into polio-free areas.

PATHOPHYSIOLOGY

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.

MORTALITY/MORBIDITY

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.

SEX

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

AGE

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

CLINICAL

HISTORY

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.

• Non-paralytic poliomyelitis or pre-paralytic poliomyelitis

  • The prodromal symptoms include generalized, non-throbbing 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.

• 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.

PHYSICAL

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

v  Muscle weakness can be assessed by muscle strength testing.

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

o    The trunk muscles are affected least.

o    Sensation should be within normal limits objectively.

o    Deep tendon reflexes are diminished or absent.

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

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

v  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.

v  Cranial nerve involvement

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

o    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.

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

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

CAUSES

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.

DIAGNOSIS

LABORATORY STUDIES

• 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

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

PROCEDURES

• 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.

TREATMENT

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.

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.

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.  

MEDICATION

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.

VACCINES

Provide active immunity against poliovirus 

SALK VACCINE (Inactivated Poliovirus Vaccine [IPV])

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.

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.

Adult: Salk vaccine for first 2 doses (Two 0.5-mL doses 4-8 wk apart), followed by a third dose administered 6-12 mo after the second 

Pediatric: IPOL - One dose (0.5 mL SC)

POLIOVAX - One dose (0.5 mL SC)

All children should receive 4 doses of IPV at 2 mo, 4 mo, 6-18 mo, and 4-6 y according to 2000 Advisory Committee on Immunization Practices (ACIP) recommendations; if accelerated protection is needed, minimal interval between doses is 4 wk 

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Avoid vaccinating during pregnancy 

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.

Pediatric: One dose of OPV (0.5 mL PO from a single dose dispenser) contained approximately 3- to 10-fold the minimal dose of virus.