Acute Flaccid Myelitis (AFM)

Acute flaccid myelitis (AFM) is a rare but serious neurologic condition. AFM is characterized by rapid onset of flaccid weakness in one or more limbs without a known cause and distinct abnormalities of the spinal cord gray matter on magnetic resonance imaging (MRI).

In addition to the limb weakness, some people may also experience one or more of the following symptoms:

gait difficulty
facial droop or weakness
difficulty moving the eyes
drooping eyelids
difficulty talking or swallowing
unable to pass urine
pain in arms, legs, and/or neck
numbness or tingling

The clinical presentation is similar to poliomyelitis, but the polio virus has not been detected in any specimens from patients with AFM.

AFM is considered a medical emergency as some patients can experience rapid respiratory failure and may require ventilator support.

Cause: There is no single known cause of AFM; all infectious and non-infectious etiologies are investigated. It has been primarily associated with viruses such as non-polio enteroviruses which typically cause mild illness such as a fever or respiratory infections. Other viruses, including flaviviruses, herpesviruses, and adenoviruses, are considered.

AFM can also resemble other conditions, including transverse myelitis and Guillain-Barré syndrome. For most reported cases across the US, the cause has not been identified. More research needs to be done to better understand why some people develop AFM after a viral infection and why others do not. Providers should consider a diagnosis of AFM in late summer or early fall, especially in patients with preceding viral symptoms.

Illness and Treatment: AFM is treated through supportive care, which is recommended by teams of expert health care providers on a case-by-case basis. The long-term effects of AFM are different for each person. Some people diagnosed with AFM recover quickly and completely. Others have continued weakness and require ongoing, high-level care.

Additional Risks: AFM appears to affect children more than adults. About 90% of acute flaccid myelitis cases affect children between the ages of 1 and 7.

Please note: All patients meeting the clinical criteria for AFM also meet the criteria for consideration as a possible paralytic poliomyelitis case, which is immediately notifiable to local health jurisdictions in Washington under WAC 246-101. Travel and immunization histories should be obtained as soon as possible on all suspected AFM cases to help rule out polio as a possible cause.

Purpose of Reporting and Surveillance

To identify cases of AFM and establish an incidence baseline and burden of the condition in Washington State.
To help identify causes of AFM in the United States.
To understand the impact of AFM among all age groups.

Legal Reporting Requirements

Heath care providers and Health care facilities: notifiable to local health jurisdiction within 24 hours
Laboratories: no requirements for reporting
Local health jurisdictions: notifiable to the Washington Department of Health (DOH) Office of Communicable Disease Epidemiology (CDE) within 7 days of case investigation completion or summary information required within 21 days. (1-206-418-5500 or 1-877-539-4344)