Acute Flaccid Myelitis (AFM) Provider Information


**Call the Maricopa County Department of Public Health at 602-506-6767 within 24 hours of identifying a suspect case of AFM**

The CDC asks that clinicians continue to be vigilant in reporting and providing information for patients that meet the clinical criteria for AFM (sudden onset of flaccid limb weakness) to their local health department. Cases that meet the clinical criteria should be reported regardless of their lab results. Patient information is needed to better understand the spectrum of AFM, possible causes, risk factors, and outcomes for this condition.

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). 

Beginning in the summer and fall of 2014, an apparent increase in reports of AFM occurred in the United States, and standardized surveillance was established in 2015 to monitor this illness and attempt to estimate the baseline incidence. Data collected since the establishment of standardized surveillance helped with the identification of another increase in reports nationally during 2016 and has provided additional valuable information on the clinical presentation to help better characterize the clinical features, epidemiology, and short-term outcomes of cases of AFM.

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Clinical Criteria

An illness with onset of acute flaccid weakness.

Laboratory Criteria

Confirmatory Laboratory Evidence:
Magnetic resonance image (MRI) showing spinal cord lesions largely restricted to the gray matter* and spanning one or more vertebral segments
Supportive Laboratory Evidence:
Cerebral spinal fluid (CSF) with pleocytosis (white blood cell count >5 cells/mm3)
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Clinically compatible case AND
Confirmatory laboratory evidence (MRI showing spinal cord lesions largely restricted to the gray matter*ꝉ and spanning one or more vertebral segments)
Clinically compatible case AND
Supportive laboratory evidence: CSF showing pleocytosis (White blood cell count >5/mm3)

Case classification will be verbally reported to the health department by the CDC.

 * 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. MRI studies performed 72 hours or more after onset should also be reviewed if available. 
 † 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.

CSTE Standardized Surveillance and Case Definition


Call the Maricopa County Department of Public Health, Office of Epidemiology 602-506-6767