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Acute Flaccid Myelitis in Children

April 25, 2017

Every year, children in the United States develop neurologic illness with limb weakness, this condition is known as Acute Flaccid Myelitis (AFM). Starting back in August 2014, CDC received an increase in reports of people across the United States with AFM for which no cause could be found. Since that time, CDC has been actively investigating this illness and continues to receive reports of sporadic cases of AFM across the country. As of December 2016, the CDC verified reports of more than 138 people in 37 states confirmed to have acute flaccid myelitis. In March 2017, the CDC updated specimen collection, shipping and testing guidance for suspected AFM cases. Questions about the guidance should be directed to limbweakness@cdc.gov.

Acute flaccid myelitis is a condition that affects the nervous system, specifically the spinal cord, which can result from a variety of causes including viral infections. This is characterized by a sudden weakness in one or more arms or legs, along with loss of muscle tone and decreased or absent reflexes. 

A patient must meet the clinical criteria below to be considered either a confirmed or probable case of acute flaccid myelitis:​

Confirmed Case 

To be considered a confirmed case, a patient must meet the following criteria: 

  • Acute onset of focal limb weakness, AND
  • An MRI showing a spinal cord lesion largely restricted to gray matter and spanning one or more spinal segments.

​Probable Case

To be considered a probable case, a patient must meet the following criteria:

  • Acute onset of focal limb weakness, AND
  • Cerebrospinal fluid (CSF) with pleocytosis (white blood cell count >5 cells/mm3, adjusting for presence of red blood cells by subtracting 1 white blood cell for every 500 red blood cells present).

​Health care providers are encouraged to review the following resources:


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