Myelitis, Acute Flaccid

Key Features

Essentials of Diagnosis

• Viral illness precedes neurologic signs

• Flaccid paralysis usually affects upper limbs or all four limbs

• Enterovirus is commonly isolated; poliomyelitis must be ruled out

General Considerations

• Before widespread polio vaccination in the 1950s, polio was the most common cause of acute flaccid myelitis (also known as acute flaccid paralysis)

• This disease has been reported throughout

  • Africa (20 countries)

  • The Eastern Mediterranean region (5 countries)

  • Intermittently in Europe (Germany and France)

  • The United States (48 states and the District of Colombia)

• The CDC began surveillance for acute flaccid myelitis in 2014

  • Since then, there have been three outbreaks in the United States

    • The largest to date occurred in 2018, with 238 confirmed cases

    • Most affected individuals had a preceding viral illness in the month before presentation of neurologic signs

• The most commonly associated viruses were enteroviruses A71 and D68

• In all instances, poliomyelitis was ruled out, but an exact cause for the acute flaccid myelitis was not always determined

• All suspected cases should be reported to the state health department, the CDC or both

Clinical Findings

• Usually a childhood disease; the average age of presentation is 5 years

• Cases usually present in late summer or early fall

• There are three clinical stages of acute flaccid myelitis

  • A prodromal illness

  • Acute neurologic injury

  • Convalescence

• Prodrome illness typically consists of

  • Fever

  • Upper respiratory symptoms

  • Gastrointestinal symptoms

• Neurologic symptoms

  • Begin 1–4 weeks later

  • Usually manifest as flaccid limb weakness with decreased reflexes

  • Fever may recur, and the patient experiences myalgia and flaccid weakness in one or more limbs

  • Upper extremities are affected more often than lower extremities

• Convalescent phase

  • Can last for months to years

  • Patients may experience residual muscle weakness and atrophy

Diagnosis

Laboratory Findings

• Cerebrospinal fluid analysis shows pleocytosis (white blood cells > 5/mcL [0.005 × 10⁹/L]) often with an elevated protein level (and a normal glucose concentration)

• All individuals with suspected acute flaccid myelitis should be tested for enteroviruses (including D68 and A71) and rhinovirus from relevant anatomic sites

• Testing for arboviruses, adenovirus, and herpesviruses should also be considered

Imaging

• MRI typically shows disease of the central gray matter within the spinal cord in the location of the anterior horn cells

• MRIs of the brain and spinal cord should be accompanied by lumbar puncture

Treatment

• No specific treatment

• Supportive care

• Many adjunctive therapies have been used, including IVIG, high-dose corticosteroids, and plasmapheresis, but none have shown efficacy

• Long-term therapy during the convalescent phase should include physical therapy and any other necessary forms of physical rehabilitation

Outcome