• Clinical science

Poliomyelitis (Polio…)


Poliomyelitis, or polio, is a disease caused by poliovirus, a type of human Enterovirus. Poliovirus spreads via fecal-oral transmission. Although the majority of poliovirus infections are asymptomatic, some may invade the central nervous system, leading to motor neuron death and irreversible paralysis that can cause respiratory insufficiency and death. The main clinical manifestations of poliomyelitis are weakness, decreased muscle tone, and hyporeflexia. The diagnosis is established based on polymerase chain reaction (PCR) findings of poliovirus RNA in cerebrospinal fluid. Poliomyelitis has been eradicated in most parts of the world thanks to the success of global vaccination initiatives. The treatment of poliomyelitis is mainly supportive. Patients with brainstem or respiratory muscle involvement may require intubation and mechanical ventilation. The majority of patients do not regain their full strength after recovery. Some patients go on to develop post-polio syndrome, a poorly understood syndrome characterized by progressive disability and muscle weakness decades after the initial polio infection.


  • Due to widespread vaccination measures, poliomyelitis has been eradicated from the United States and most other countries.
  • Poliovirus is still endemic in Afghanistan, Nigeria, and Pakistan.

Epidemiological data refers to the US, unless otherwise specified.


  • Causative agent
  • Transmission route
    • Fecal-oral route: absorption of poliovirus in the intestinal tract
    • Rarely, droplet transmission may occur during epidemics.
  • Incubation time
    • 7–14 days


Clinical features

Over 90% of infections with poliovirus are asymptomatic. Clinical infection is observed in less than 10% of cases and less than 1% of infected individuals develop paralysis. The clinical forms of poliomyelitis are:

Poliomyelitis without CNS involvement (abortive poliomyelitis) (4–8% of cases)

Poliomyelitis with CNS involvement

Nonparalytic poliomyelitis: aseptic meningitic form (1–2% of cases)

  • Clinical findings
    • Begins several days following abortive poliomyelitis (often temporary, symptom-free interval)
    • Fever, neck stiffness, headache, vomiting, muscle pain
    • Neck muscle weakness (head drop sign: head falls back when placed in a supine position)
    • No paresis!
  • Cerebrospinal fluid (CSF) diagnostics: lymphocytic pleocytosis, normal glucose levels, and normal or slightly elevated protein levels

Paralytic poliomyelitis (less than 1% of cases)

  • Clinical findings
    • Occurs 2–3 days; following the meningitic form after a brief symptom-free interval
    • Fever
    • Severe back, neck, and muscle pain
    • Asymmetric flaccid paralysis worsens over hours to days
    • Most commonly affects the leg muscles, although the arms, abdomen, trunk, thorax, and eyes may be affected
    • Paralysis is usually more severe in proximal muscles than in distal muscles.
    • Diminished deep tendon reflexes
  • Complications
    • Ascending paralysis with diaphragmatic involvement respiratory failure
    • Bulbar form with brain stem involvement (rare): damage to the cerebral or autonomic nerve centers (cranial nerves and respiratory center) → central respiratory paralysis


Subtypes and variants

Post-polio syndrome (post-poliomyelitis syndrome, PPS)

  • Most frequent complication observed following poliovirus infection (up to 40% of survivors)
  • Occurs decades after infection
  • Manifests with progressive muscle weakness and pain, even in areas that were not affected by the initial infection




Differential diagnoses

The differential diagnoses listed here are not exhaustive.



  • The prognosis is dependent on the form of poliomyelitis.
  • In the abortive and nonparalytic forms, complete recovery without complications occurs within 2 weeks.
  • In the paralytic form, the most serious short-term risk is death due to diaphragmatic involvement. After recovery, most patients have residual deficits, including muscle weakness or contractures and muscle pain.
  • Post-polio syndrome may lead to muscle weakness and pain decades after polio infection.



  • The inactivated poliovirus vaccine (IPV) is recommended for childhood immunization in the United States and most high-income countries.
  • In the US, children receive 4 doses of IPV, at 2, 4 and 6–18 months; , followed by a booster dose at 4–6 years; . See immunization schedule.
  • The live attenuated oral poliovirus vaccine (OPV) is used for childhood immunization in low-income countries because it is less costly. It has a slightly increased risk of vaccine-associated paralytic polio and is being gradually replaced in favor of the IPV worldwide.