CDC Resources for Acute Flaccid Myelitis

PUBLISHED: Oct 9, 2018
Relevant to: All Healthcare Organizations

Acute flaccid myelitis (AFM) is a syndrome characterized by rapid onset of flaccid weakness in one or more limbs and distinct abnormalities of the spinal cord gray matter on magnetic resonance imaging (MRI). While not a new condition, beginning in the summer and fall of 2014, the U.S. Centers for Disease Control and Prevention (CDC) began receiving an increase in reports of AFM in the United States. Standardized surveillance was established in 2015 to monitor this illness and attempt to estimate occurrence.

In June 2015, the Council of State and Territorial Epidemiologists (CSTE) adopted a standardized case definition for AFM that is used by CDC to classify suspected cases as confirmed or probable.

Case Classification:


  • Clinically compatible case AND
  • Confirmatory laboratory evidence: MRI showing spinal cord lesion largely restricted to gray matter and spanning one or more spinal segments (note: Spinal cord lesions may not be present on initial MRI; a negative or normal MRI performed within the first 72 hours after onset of limb weakness does not rule out AFM; Terms in the spinal cord MRI report such as “affecting mostly gray matter,” “affecting the anterior horn or anterior horn cells,” “affecting the central cord,” “anterior myelitis,” or “poliomyelitis” would all be consistent with this terminology.)


  • Clinically compatible case AND
  • Supportive laboratory evidence: CSF showing pleocytosis (white blood cell count >5 cells / mm)

According to the CDC, clinicians should continue to be vigilant and send all information about patients that meet the clinical criteria for AFM to their state or local health department. Clinicians should send information on patients who meet the clinical criteria regardless of any laboratory results or MRI findings.

The CDC has developed, with input from an expert group of neurologists, infectious disease experts, pediatricians, immunologists, and public health experts, a document with considerations for clinical management of patients with AFM. These considerations are encouraged by this expert group to be used by healthcare providers for clinical management of AFM. A link to the document is provided below.

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