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Emergency And Acute Medicine – Polio
Polio is caused by infection with poliovirus. The incubation period is typically 7–14 days, and the duration of acute illness is usually less than 1 week. Clinical manifestations vary widely. Approximately 90–95% of infections are subclinical and not clinically apparent. Abortive poliomyelitis accounts for 4–8% of cases and presents as a nonspecific viral illness with fever, myalgias, and malaise; it is often recognized as polio only during outbreaks. Nonparalytic poliomyelitis occurs in 1–2% of cases and resembles aseptic meningitis, with meningeal irritation and a similar clinical course. Paralytic poliomyelitis occurs in about 0.1% of infections and is subdivided into spinal, bulbar, and mixed bulbospinal forms. Spinal paralytic poliomyelitis causes asymmetric flaccid paralysis, more prominent in the lower extremities. Bulbar involvement, seen in about 10% of paralytic cases, affects cranial nerve–innervated muscles and may compromise respiratory and circulatory centers, resulting in high mortality. Postpoliomyelitis syndrome is characterized by new-onset weakness, pain, and atrophy occurring 8–70 years after the initial illness, usually in previously affected limbs, and progresses gradually.
Poliovirus is a small, nonenveloped RNA virus in the enterovirus genus of the Picornavirus family. There are three subtypes (1, 2, and 3). Transmission occurs via the fecal–oral route. The virus enters through the oral cavity and replicates in the pharynx, gastrointestinal tract, and lymphatic tissue. Humans are the only natural host and reservoir. The virus selectively destroys motor and autonomic neurons. Wild-type poliovirus has been eliminated in the United States since 1979. In the United States, prior cases were associated with the oral poliovirus vaccine (OPV), which could rarely undergo neurovirulent conversion, resulting in vaccine-associated paralytic poliomyelitis (VAP). With the widespread use of inactivated poliovirus vaccine (IPV), VAP has markedly decreased. OPV remains in use in some regions as part of global eradication efforts.
Most infections are asymptomatic. Symptomatic cases may present with fever, headache, malaise, sore throat, fatigue, nausea, and vomiting. Nonparalytic disease manifests with stiff neck and back pain consistent with aseptic meningitis. Paralytic disease is characterized by progressive weakness lasting less than one week, sometimes accompanied by dysphagia and dysarthria in bulbar involvement. In children, a biphasic course is more common, with an initial viral prodrome lasting 1–2 days, followed by a symptom-free interval of 2–5 days, and then abrupt onset of major neurologic illness.
History should include vaccination status, prior polio infection, recent exposure to individuals vaccinated with OPV, recent travel to endemic areas such as Nigeria, Pakistan, India, or Afghanistan, and comorbid immunocompromising conditions, particularly B-cell disorders. On physical examination, patients may have low-grade fever, headache, photophobia, and nuchal rigidity. Neurologic findings include severe muscle soreness progressing to flaccid weakness and asymmetric paralysis, typically greater in the lower extremities. Reflexes may be initially hyperactive and later absent. Sensory function remains intact. Urinary retention occurs in approximately half of paralytic cases. Patients may appear apprehensive and irritable.
Diagnosis is primarily clinical and requires differentiation from other causes of acute flaccid paralysis. Public health authorities must be notified when polio is suspected. Laboratory findings may show normal or mildly elevated white blood cell count. Confirmation is achieved by demonstrating a rise in antibody titers between acute and convalescent sera or by isolating the virus from blood, cerebrospinal fluid, stool, or throat secretions during the first week of infection. Cerebrospinal fluid analysis typically shows findings consistent with aseptic meningitis, including lymphocytic pleocytosis and elevated protein, although the virus is rarely isolated from CSF. Electrodiagnostic studies demonstrate motor involvement with preserved sensory function.
The differential diagnosis depends on the clinical form. Abortive disease resembles other viral illnesses. Nonparalytic disease is indistinguishable from other causes of aseptic meningitis. Paralytic disease must be differentiated from Guillain–Barré syndrome, acute transverse myelitis, spinal cord compression or infarction, multiple sclerosis, amyotrophic lateral sclerosis, rhabdomyolysis, acute intermittent porphyria, West Nile virus infection, diphtheria, botulism, tick paralysis, and encephalitis.
Management is supportive. Fatal cases are usually due to respiratory insufficiency, which requires prompt recognition and ventilatory support. Aggressive pulmonary toilet and early intubation are indicated when respiratory compromise develops. Treatment includes bed rest to reduce risk of worsening paralysis and analgesics for severe muscle pain and spasm. Unnecessary intramuscular injections or tissue injury should be avoided, as paralysis may localize to recently traumatized limbs. There are no effective antiviral agents.
Prevention is achieved through vaccination. Inactivated poliovirus vaccine is currently used in the United States and does not cause vaccine-associated disease. Oral poliovirus vaccine, though no longer used in the United States, remains part of global eradication programs because of its ability to confer community immunity through fecal–oral spread.
All patients with acute-phase paralytic poliomyelitis require hospital admission for strict bed rest and close monitoring for respiratory involvement. Isolation from unvaccinated individuals is necessary. Patients without nervous system involvement and without risk of contact transmission may be discharged. Physical therapy is essential during recovery, although only about one-third of patients with acute flaccid paralysis regain full strength. Postpolio syndrome may occur decades later with progressive neuromuscular symptoms.
Key clinical points include the wide spectrum of presentation from asymptomatic infection to acute flaccid paralysis, the importance of vaccination history and travel exposure, the need for early respiratory monitoring in paralytic cases, and the primarily supportive nature of treatment.
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