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Frequently Asked Questions

Q: What is acute flaccid myelitis (AFM)?

A: AFM is a syndrome characterized by sudden onset of limb weakness, sometimes accompanied by cranial nerve dysfunction (such as facial drooping or difficulty speaking). In many cases, distinctive lesions in the gray matter (nerve cells) of the spinal cord may be seen on neuroimaging.

Q: What causes AFM?

A: A number of infectious germs have been demonstrated to cause AFM, including poliovirus and other non-polio enteroviruses, flaviviruses (such as West Nile Virus), and adenoviruses. A condition where the body’s immune system attacks and destroys body tissue that it mistakes for foreign material may also cause AFM.

Q: Were the AFM cases in 2014 related to the outbreak of severe respiratory illness caused by enterovirus-D68 (EV-D68)?

A: In August 2014, physicians in Colorado noted an unusual cluster of acute flaccid myelitis among children. This cluster occurred around the same time as an increase in cases of severe respiratory illness caused by EV-D68. This strong temporal association (the cluster of AFM cases occurring at the same time as the EV-D68 respiratory outbreak) led many to suspect that the cluster of AFM cases might also have been caused by EV-D68. It is biologically plausible that EV-D68 could have caused the cases of AFM in 2014, as other enteroviruses have been demonstrated to cause AFM. Also, EV-D68 has been previously identified in clinical specimens from a few patients with AFM. In those cases however, it is not clear whether the presence of EV-D68 was a coincidence or whether it was the cause of the AFM. Regardless, extensive testing of clinical specimens from AFM cases in 2014 did not find a clear and consistent pathogen.

Q: How can I send information about a case of AFM?

A: If you believe you or your child has symptoms that are compatible with AFM, please contact your doctor as soon as possible. Because AFM can be a severe illness, your doctor can help you determine next steps.

Q: Will CDC conduct extended follow-up on cases of AFM after their initial clinical presentation?

A: Currently CDC is considering the most efficient ways of following up on cases of AFM detected through routine information gathering and close collaboration with state and local health departments and institutions caring for these affected children. CDC conducted a short-term follow-up survey on cases with information collected during the 2014 investigation, and received responses from roughly half (56) of the identified cases. A small number described complete recovery of limb function after a median of about 4 months after onset of limb weakness. The majority described some improvement of function, though it is not clear how much improvement occurred. A small number described no improvement in limb function. No deaths were noted.

Q: How does AFM differ from other conditions that have limb weakness, such as Guillain-Barré Syndrome (GBS)?

A: While many of the signs and symptoms of AFM may be similar to other conditions that have limb weakness, such as GBS, AFM is characterized by distinctive MRI findings specific to the spinal cord gray matter. Upon more detailed testing, the differences between AFM and other conditions that cause limb weakness can be readily distinguished. Treatment, prognosis, and diagnostic testing also differ for AFM, so it is important to get the patient to a doctor with neurologic experience as quickly as possible after onset of unexplained limb weakness.

Q: Is it possible that patients with AFM are being misdiagnosed with other illnesses?

A: AFM is diagnosed based on a combination of clinical symptoms and specific laboratory or MRI findings. We are still trying to determine the full spectrum of illness that may present as AFM, such as acute transverse myelitis or Guillain-Barré syndrome, which can present in an identical fashion to AFM. CDC and local partners are working as hard as possible to determine diagnostic criteria that would easily distinguish AFM from these other forms of acute flaccid paralysis. Therefore, it is possible that a case of AFM may be misdiagnosed as another illness. In the current setting, however, we expect that this occurrence would be rare.

For more information on AFM, visit the About AFM page.

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