What should I know about acute flaccid myelitis (AFM)?

Picture of Enterovirus D68 (EV-D68)
Picture of Enterovirus D68 (EV-D68)

*Acute flaccid myelitis (AFM) facts written by Charles P. Davis, MD, PhD

What is the medical definition of acute flaccid myelitis (AFM)?
Acute flaccid myelitis is a rare condition of the nervous system that causes the muscles and reflexes of the body to weaken. Viruses, toxins, and genetic disorders can all cause acute flaccid myelitis. Viruses that can cause the condition or similar symptoms include poliovirus, non-polio enteroviruses, adenovirus, or West Nile virus. The exact cause of most cases is not definitively known. However, development of acute flaccid myelitis is extremely rare. It is estimated that less than one in 1 million people in the US develop this condition every year. Symptoms are a sudden onset of arm or leg weakness and loss of muscle tone and reflexes. Other symptoms can include facial droop, eyelid droop, difficulty moving the eyes, facial weakness, slurred speech, or problems with swallowing. Respiratory failure is the most serious potential symptom. Even though the condition is very rare, the US CDC has received reports of an increasing number of cases of acute flaccid myelitis since 2014; most of the reported cases have occurred in children.

How do I know if I have/What are the early signs of acute flaccid myelitis (AFM)?

  • Acute flaccid myelitis (AFM) is a rare but serious problem with the nervous system in the area of the spinal cord (gray matter) that causes muscles and reflexes in the body to become weak. The condition began increasing in frequency in 2014. It occurs mainly in children and very rarely in adults. AFM is not contagious from person to person but may spread to humans from mosquitoes.
  • AFM symptoms and signs usually have a sudden onset that begins with arm or leg weakness along with loss of muscle tone and reflexes. In addition, patients may have facial droop difficulty moving their eyes drooping eyelids, and/or difficulty with swallowing or speaking (slurred speech), with the most severe symptom being a respiratory failure.

How do I know if I have acute flaccid myelitis (AFM)?

  • Viruses, environmental toxins, and/or genetic disorders may cause AFM and similar neurological conditions. Viruses that may cause AFM or similar conditions are poliovirus and non-polio enteroviruses (especially enterovirus 68), West Nile virus, Japanese encephalitis, St. Louis encephalitis, and adenoviruses. AFM often has no identifiable cause despite lab tests.
  • Tests that doctors use to diagnose AFM include a detailed physical exam the person's nervous system and a review of spinal cord images with CT/MRI. In addition, medical professionals perform other lab tests on the cerebrospinal fluid (for example, detection of viruses) because AFM shares many of the same symptoms as other neurological diseases such as transverse myelitis or Guillain-Barré syndrome. Some neurologists may do nerve conduction tests.

How do I get rid of acute flaccid myelitis (AFM)?

  • Unfortunately, there is no specific treatment for AFM. Some neurologists may recommend physical and occupational therapy, but the long-term prognosis and recovery from AFM are unknown.

About Acute Flaccid Myelitis

Acute flaccid myelitis (AFM) is a rare but serious condition. It affects the nervous system, specifically the area of spinal cord called gray matter, which causes the muscles and reflexes in the body to become weak. This condition is not new, but the increase in cases we saw starting in 2014 is new. Still, CDC estimates that less than one in a million people in the United States will get AFM every year. There are a variety of possible causes of AFM, such as viruses, environmental toxins, and genetic disorders. Most of the cases that CDC has learned about have been in children.

Sign of Acute Flaccid Myelitis

Drooping Eyelids (Ptosis)

A drooping or sagging of the eyelid is medically known as ptosis or blepharoptosis. Drooping eyelids may occur on both sides (bilateral) or on one side only (unilateral), in which case it is more easily noticed. Congenital ptosis is eyelid drooping that is present at birth; when it develops later, it is referred to as acquired ptosis. Depending upon the severity of the condition, drooping eyelids may be barely noticeable or quite prominent.


Most people will have sudden onset of arm or leg weakness and loss of muscle tone and reflexes. Some people, in addition to arm or leg weakness, will have:

  • facial droop/weakness,
  • difficulty moving the eyes,
  • drooping eyelids, or
  • difficulty with swallowing or slurred speech.

Numbness or tingling is rare in people with AFM, although some people have pain in their arms or legs. Some people with AFM may be unable to pass urine (pee). The most severe symptom of AFM is respiratory failure that can happen when the muscles involved with breathing become weak. This can require urgent ventilator support (breathing machine). In very rare cases, it is possible that the process in the body that triggers AFM may also trigger other serious neurologic complications that could lead to death.

If you or your child develops any of these symptoms, you should seek medical care right away. Your doctor may collect information about your symptoms and send this information to their health departments. This is because CDC is asking doctors to be alert for patients with symptoms of AFM so that we can learn more about this condition.


Acute Flaccid Myelitis (AFM) See pictures of viral infections See Images

Possible Causes of AFM

AFM or similar neurologic conditions may have a variety of possible causes such as viruses, environmental toxins, and genetic disorders.

Certain viruses that can cause AFM or similar neurologic conditions are

Oftentimes, despite extensive lab tests, the cause of a patient's AFM is not identified.


AFM is diagnosed by examining a patient's nervous system in combination with reviewing pictures of the spinal cord. A doctor can examine a patient's nervous system and the places on the body where he or she has a weakness, poor muscle tone, and decreased reflexes. A doctor can also do an MRI (magnetic resonance imaging) to look at a patient's brain and spinal cord, do lab tests on the cerebrospinal fluid (the fluid around the brain and spinal cord) and may check nerve conduction (impulse sent along with a nerve fiber) and response. It is important that the tests are done as soon as possible after the patient develops symptoms.

AFM can be difficult to diagnose because it shares many of the same symptoms as other neurologic diseases, like transverse myelitis and Guillain-Barre syndrome. With the help of testing and examinations, doctors can distinguish between AFM and other neurologic conditions.


West Nile Virus Infection: Causes, Symptoms, and Treatment See Slideshow


There is no specific treatment for AFM, but a doctor who specializes in treating brain and spinal cord illnesses (neurologist) may recommend certain interventions on a case-by-case basis. For example, neurologists may recommend physical or occupational therapy to help with arm or leg weakness caused by AFM. We do not know the long-term outcomes (prognosis) of people with AFM.

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Poliovirus and West Nile virus may sometimes lead to AFM.

  • You can protect yourself and your children from poliovirus by getting vaccinated.
  • You can protect against bites from mosquitoes, which can carry the West Nile virus, by using mosquito repellent, staying indoors at dusk and dawn (when bites are more common), and removing standing or stagnant water near your home (where mosquitoes can breed).

While we don't know if it is effective in preventing AFM, washing your hands often with soap and water is one of the best ways to avoid getting sick and spreading germs to other people. Learn about when and how to wash your hands.

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United States. Centers for Disease Control and Prevention. "Acute Flaccid Myelitis." Apr. 2, 2018. <https://www.cdc.gov/acute-flaccid-myelitis/about-afm.html>.