After an incubation period of 3-6 days, ~5% of pts present with a minor illness (abortive poliomyelitis), characterized by fever, malaise, sore throat, myalgias, and headache, that usually resolves within 3 days.

• Asymptomatic infection: >90% of all infections
• Aseptic meningitis (nonparalytic poliomyelitis): occurs in ~1% of pts. Examination of CSF reveals normal glucose and protein concentrations and lymphocytic pleocytosis (with PMNs sometimes predominating early).
• Paralytic disease: the least common form; presents ≥1 day after aseptic meningitis as severe back, neck, and muscle pain as well as gradually developing motor weakness
  • - The weakness is usually asymmetric and proximal and is most common in the legs. The arms and the abdominal, thoracic, and bulbar muscles are also frequently involved.
  • - Paralysis generally occurs only during the febrile phase.
  • - Physical examination reveals weakness, fasciculations, decreased muscle tone, and reduced or absent reflexes in affected areas; hyperreflexia may precede the loss of reflexes. Bulbar paralysis is associated with dysphagia, difficulty handling secretions, or dysphonia.
  • - Respiratory insufficiency due to aspiration or neurologic involvement may develop. Severe medullary infection may lead to circulatory collapse.
  • - Most pts recover some function, but around two-thirds have residual neurologic sequelae.
• Vaccine-associated poliomyelitis: The risk of acquiring poliomyelitis after vaccination with the live oral vaccine is estimated to be 1 case per 2.5 million doses and is ~2000 times higher among immunodeficient persons, especially pts with hypo- or agammaglobulinemia.
• Postpolio syndrome: new weakness 20-40 years after poliomyelitis. Onset is insidious, progression is slow, and plateau periods can last 1-10 years.