Update on Acute Flaccid Myelitis

Manisha Patel, MD, MS


March 22, 2017

Editorial Collaboration

Medscape &

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Hello. I'm Dr Manisha Patel, a medical officer with the Centers for Disease Control and Prevention (CDC). Today, as part of the CDC Expert Commentary series on Medscape, I'll provide an update on acute flaccid myelitis (AFM), which we've been investigating since 2014 when we received an increase in reports in the United States. I'll also share with you recent changes to CDC's guidance for specimen collection and lab testing.

AFM is a rare condition that affects the nervous system, specifically the spinal cord. It causes sudden weakness or loss of muscle tone and reflexes in the arms or legs. In addition, some patients may have facial droop or weakness, difficulty moving the eyes, ptosis, or difficulty with swallowing or slurred speech. Conditions like AFM can have many different causes, including viral infections, environmental toxins, and genetic disorders.

In 2016, we've received an increase in reports and observed a seasonal peak similar to that in 2014. From January to October 2016, a total of 108 people, mostly children younger than 18 years of age, in 36 states were confirmed to have AFM.[1] Even with this increase, AFM remains very rare-fewer than one in a million people. Despite extensive pathogen-specific testing of many specimens since 2014, we still don't know what caused these people to get AFM. However, their symptoms are most similar to those of people who have rare complications from viruses such as poliovirus and West Nile virus.

CDC continues to investigate each case of AFM to understand the causes and risk factors. We recently expanded our testing for potential infectious and noninfectious causes, including, possibly, immune-mediated mechanisms. To optimize this new approach, CDC will no longer be performing clinical diagnostics for enteroviruses or metagenomic sequencing on specimens from suspect AFM cases, as testing to date has not identified any consistent pathogen.

What do clinicians need to know now? Updated recommendations[2] focus on the following changes to our lab guidance and testing procedures:

  • First, we have updated our guidance for collecting, storing, and shipping cerebrospinal fluid, blood, and stool specimens collected from suspected AFM cases. It is important to note that specimens should be shipped ideally within 24 hours of collection to ensure optimal results for our new testing protocols. Detailed information is on the CDC's AFM website.

  • Second, we are no longer requesting respiratory specimens. However, we will perform genotyping on respiratory specimens that have already tested positive for enteroviruses or rhinoviruses at external laboratories. It is also important to collect stool specimens to rule out the presence of poliovirus so that we can demonstrate maintenance of elimination in the United States. This is important as we continue to support efforts for the global eradication of polio.

  • Last, because the new testing that will be done at CDC uses assays that are not CLIA-approved and are not intended for clinical diagnosis, CDC will not be providing individual clinical reports of specific test results. Results that indicate a possible cause of AFM, however, will be rapidly disseminated to health departments and providers when available.

While we continue to investigate AFM, clinicians can help protect their patients from certain viruses, such as poliovirus and West Nile virus, that very rarely may lead to conditions like AFM. Prevention is basic: making sure that patients are up-to-date on polio vaccinations and advising patients to use mosquito repellent. In general, good hand hygiene practices will also help reduce the risk for and spread of infections from various pathogens that could potentially cause AFM.

We encourage clinicians to continue to be vigilant for patients with neurologic symptoms like those caused by AFM, and to collect specimens from patients suspected of having AFM as early as possible in the course of illness, preferably on the day of onset of limb weakness. Like I mentioned previously, specimens include cerebrospinal fluid, blood (including serum and whole blood), and two stool specimens collected as soon as possible after onset of limb weakness and separated by 24 hours.

All suspected AFM cases should be reported to your local or state health departments. Health departments should then report these cases to CDC using a patient summary form, which is available on CDC's website and can be found by typing "CDC AFM data collection form" in your search engine. Health departments should report patients who meet the clinical case definitions regardless of any laboratory results.

For more information, or for questions about AFM, please visit CDC's website or send an email to

Acute Flaccid Myelitis in the United States-August - December 2014: Results of Nation-Wide Surveillance
Notice to Clinicians: Continued Vigilance Urged for Cases of Acute Flaccid Myelitis, COCA Clinical Reminder
CDC: Investigation of Acute Neurologic Illness with Focal Limb Weakness of Unknown Etiology in Children
Notes from the Field: Acute Flaccid Myelitis Among Persons Aged ?21 Years- United States, August 1-November 13, 2014
Acute Neurologic Illness of Unknown Etiology in Children - Colorado, August-September, 2014

Manisha Patel, MD, MS, is a pediatric infectious disease physician and epidemiologist, and has been with the Centers for Disease Control and Prevention since 2010. She serves as the Team Lead for the Vaccine Preventable Viral Diseases Branch at CDC's National Center for Immunizations and Respiratory Diseases. Her areas of expertise include measles, mumps, rubella, polio, cytomegalovirus, and acute flaccid myelitis. Her previous work included policy, immunology, and outbreak response for pertussis and meningococcal disease. She is also a practicing pediatrician in Atlanta, Georgia.