Acute flaccid myelitis (AFM) is an uncommon, but life-threatening neurologic condition that affects mostly children and can lead to permanent paralysis. Enteroviruses, particularly EV-D68, are likely responsible for the increase in cases every two years since 2014. AFM is a medical emergency and patients must be hospitalized and monitored in case they progress to respiratory failure. Prompt recognition and immediate action by pediatricians, and emergency department and urgent care providers are critical to achieving the best possible outcomes.

• AFM typically presents with sudden limb weakness. Most patients had respiratory illness or fever before AFM onset.
• Patient health can decline quickly, resulting in paralysis or the need for a ventilator. AFM can lead to permanent disability.
• Patients who tested positive for EV-D68 typically had more severe AFM illness, requiring hospitalized intensive care and ventilation.
• Most cases occur between August and November.

Acute flaccid myelitis (AFM) is a rare disease that affects the spinal cord, the part of the nervous system that carries messages to and from the brain. Symptoms of AFM include sudden (acute) weakness in the arm(s) or leg(s), along with loss of muscle tone and decreased or absent reflexes. Some people with AFM report pain. In some cases, AFM can affect the nerves controlling the head and neck, causing facial weakness, drooping of the eyelids, and difficulty swallowing, speaking, or moving the eyes. The most serious complication of AFM is respiratory failure if the muscles involved with breathing become weakened. Most cases of AFM have been in children, but it can develop in adults.

Many times symptoms of AFM develop after a viral infection, such as poliovirus, West Nile virus, and adenovirus. In some cases no clear possible cause is found. In addition, even when associated with a viral infection, it is not known how the infection triggers AFM, and it is not clear why some people develop AFM after an infection and others do not.

AFM can be difficult to diagnose because the symptoms are similar to other neurological diseases, such as Guillain-Barre syndrome (GBS), acute disseminated encephalomyelitis (ADEM), and transverse myelitis. Diagnosis may include a physical exam, an MRI of the spine, testing of the cerebral spinal fluid (CSF), and tests checking nerve speed (nerve conduction velocity; NCV) and the response of muscles to the messages from the nerves (electromyography; EMG).

To prevent infections by AFM-related viruses , specialists recommend staying up-to-date with polio vaccines and to minimize exposure to mosquitoes. There is no specific treatment for AFM. Treatments that have been tried include immunoglobulin, corticosteroids, plasma exchange, and antiviral therapy, but there is no clear evidence that any of these treatments affect recovery. Other treatment is supportive and depends on the symptoms. Physical therapy and occupation therapy are especially important during recovery. The extent of recovery varies. Although some people may make a full recovery, most have continued muscle weakness even after a year. Long term outcomes are not known.

What is acute flaccid myelitis (AFM)?

Acute flaccid myelitis (AFM) is a neurologic disease. It is rare, but serious. It affects an area of the spinal cord called gray matter. This can cause the muscles and reflexes in the body to become weak.

Because of these symptoms, some people call AFM a "polio-like" illness. But since 2014, people with AFM have been tested, and they did not have poliovirus.

What causes acute flaccid myelitis (AFM)?

Researchers think that viruses, including enteroviruses, likely play a role in causing AFM. Most people with AFM had a mild respiratory illness or fever (like you would get from a viral infection) before they got AFM.

Who is at risk for acute flaccid myelitis (AFM)?

Anyone can get AFM, but most cases (more than 90%) have been in young children.

What are the symptoms of acute flaccid myelitis (AFM)?

Most people with AFM will suddenly have:

• Arm or leg weakness
• A loss of muscle tone and reflexes

Some people also have other symptoms, including:

• Facial drooping/weakness
• Trouble moving the eyes
• Drooping eyelids
• Trouble swallowing
• Slurred speech
• Pain in the arms, legs, back, or neck

Sometimes AFM can weaken the muscles that you need for breathing. This can lead to respiratory failure, which is very serious. If you get respiratory failure, you may need to use a ventilator (breathing machine) to help you breathe.

If you or your child develops any of these symptoms, you should get medical care right away.

How is acute flaccid myelitis (AFM) diagnosed?

AFM causes many of the same symptoms as other neurologic diseases, such as transverse myelitis and Guillain-Barre syndrome. This can make it difficult to diagnose. The doctor may use many tools to make a diagnosis:

• A neurologic exam, including looking at where there is weakness, poor muscle tone, and decreased reflexes
• An MRI to look at the spinal cord and brain
• Lab tests on the cerebrospinal fluid (the fluid around the brain and spinal cord)
• Nerve conduction and electromyography (EMG) studies. These tests check nerve speed and the response of muscles to the messages from the nerves.

It is important that the tests are done as soon as possible after the symptoms start.

What are the treatments for acute flaccid myelitis (AFM)?

There is no specific treatment for AFM. A doctor who specializes in treating brain and spinal cord illnesses (neurologist) may recommend treatments for specific symptoms. For example, physical and/or occupational therapy may help with arm or leg weakness. Researchers do not know the long-term outcomes of people with AFM.

Can acute flaccid myelitis (AFM) be prevented?

Since viruses likley play a role in AFM, you should take steps to help prevent getting or spreading viral infections by:

• Washing hands often with soap and water
• Avoiding touching your face with unwashed hands
• Avoiding close contact with people who are sick
• Cleaning and disinfecting surfaces that you frequently touch, including toys
• Covering coughs and sneezes with a tissue or upper shirt sleeve, not hands
• Staying home when sick

What can I do if I suspect AFM?

• Seek medical care immediately if you or your child develops any of these symptoms: weakness or loss of muscle tone or reflexes in the arms or legs, facial droop or weakness, difficulty moving the eyes, drooping eyelids, difficulty with swallowing, or slurred speech.
• If your clinician suspects you or your child has AFM, they should hospitalize immediately. AFM can progress rapidly and sometimes require machines to help patients breathe.

Possible Causes

Why does CDC now believe that viruses play a role in AFM?

• CDC has been tracking AFM since 2014. This has contributed important evidence to support a role for viruses, including enteroviruses, in AFM. For example,
  • We’ve seen a seasonal pattern to AFM. Most patients develop AFM in late summer or early fall. At this same time of year, many viruses, including enteroviruses, commonly circulate in the U.S.
  • Most patients had respiratory symptoms or fever consistent with a viral infection less than a week before limb weakness began.
• Our work will help lead to more answers about this complex illness, such as why some people develop AFM, and why outbreaks happen.

Recent research has indicated that enteroviruses are the likely cause of AFM. Does CDC believe this as well?

• AFM can be caused by viruses, including enteroviruses.
• Studies have shown that AFM patients had antibodies specific for enteroviruses in their spinal fluid more often than persons without AFM. Having antibodies for enterovirus means that a person was previously infected with the virus. This is an important step toward understanding how AFM develops and why some children are severely affected.
• CDC’s partnerships with other institutions, such as universities, federal agencies, and health departments, are important to better understand AFM and these outbreaks.

How is AFM different from polio?

• Poliomyelitis is the term used to describe the syndrome of acute flaccid limb weakness and lesions in the grey matter of the spinal cord. Poliomyelitis caused by poliovirus no longer occurs in the United States. In 2014, the term AFM was adopted to describe poliomyelitis without a known cause and not caused by poliovirus.
• We now have stronger evidence that points to AFM being caused by non-polio enteroviruses, such as EV-D68 and EV-A71. Poliovirus can be prevented by a vaccine. However, there is no vaccine yet available for EV-A71 in the United States, and no vaccine for EV-D68 or for the other enteroviruses that are believed to cause AFM.
• All the stool specimens from AFM patients that we received tested negative for poliovirus. We continue to test all specimens from AFM patients to look for viruses, including poliovirus and non-polio enteroviruses.

Is there an immune response that could trigger AFM?

• CDC continues to work toward learning why some people develop AFM, including if a virus leads to an inflammatory or immune response directed toward motor neurons (nerves that make the muscles move).

Is there a link between vaccinations and AFM?

• CDC has no evidence to suggest that vaccinations cause AFM.
• Of the AFM cases reviewed in 2018, about 85% had no recorded vaccinations in the 30 days prior to the beginning of their limb weakness.
• We continue to review past medical history of all cases, including past vaccinations, as part of our work.
  • In 2018, AFM occurred in children who had received vaccines, and also in children who had received no vaccines. CDC will conduct further research using medical and vaccination histories to examine this question.
  • In a 2016 study of 10 confirmed cases of AFM in children, 9 had received all childhood vaccines recommended by the Advisory Council on Immunization Practices. When vaccine records were examined, the average amount of time between when they got their last vaccine and when they started to experience AFM symptoms (i.e., limb weakness), was almost 2 years.

Health Outcomes

Has anyone died from AFM?

• Two patients with confirmed AFM died soon after developing AFM, one in 2017 and one in 2020. We have also learned of deaths in cases confirmed in previous years.
• CDC is gathering information on deaths reported to us from health departments. We are also gathering information as part of our patient outcome data collection. We ask that health departments send information about every death of an AFM case to CDC.

When will CDC or state health departments follow up with all patients?

• CDC has implemented a systematic process for determining the patients’ outcomes at 2, 6, and 12 months after limb weakness began.
• We are currently interviewing confirmed and probable cases from 2018 and will be interviewing these cases in subsequent years moving forward. We are also going to be reaching out to confirmed cases from 2014 – 2017.

Surveillance

Why was there no outbreak of AFM in 2020?

• There have been increases in AFM cases in 2014, 2016, and 2018 across the U.S. Based on this pattern we anticipated an increase in cases in 2020, but we did not see that. CDC believes prevention measures such as social distancing, mask wearing, and increased hand washing may have reduced the circulation of enteroviruses that can cause AFM.
• We continue to monitor reported AFM cases closely and stay prepared to respond to any increase in cases.

How are AFM cases reported to CDC?

• All health departments have some type of requirement for clinicians to report suspected AFM cases. The steps for reporting are:

• The health department works with healthcare providers to collect medical information and spinal cord MRI images.
• The health department then sends this information to CDC.
• Once we receive a report from the health department, the patient summary form and spinal cord images are reviewed by experts and given a case classification based on the AFM surveillance case definition.
• Once we’ve made a final case classification, we send that information to the health department who then shares with the clinician, and the clinician shares it with the patient and their family. Clinicians should not wait for CDC’s case classification to diagnose or treat their patient.

• To protect patient privacy, CDC does not receive patient information such as names, so we are not able to tell whether a specific patient’s records have been sent to us. We strongly encourage you to reach out to your state health department if you have questions about whether your child has been reported to CDC. If you are unable to reach your health department, please contact us at AFMQuestions@cdc.gov.

How do we know every case of AFM is being recognized?

• AFM is not nationally notifiable, but all jurisdictions have some type of requirement for clinicians to report patients under investigation (PUIs) for AFM cases. Some have made AFM reportable, some require reporting of acute onset of flaccid paralysis without other apparent cause, and some require reporting of new or emerging conditions of public health importance, like AFM.

• CDC does not decide which diseases are nationally notifiable, but we do advise the Council of State and Territorial Epidemiologists and make recommendations about which diseases should be nationally notifiable.
• In June 2019, it was proposed that AFM be made nationally notifiable at the Council of State and Territorial Epidemiologists (CSTE) annual meeting. The proposal did not pass.
• State and local health departments, CSTE, and CDC, will continue to collaborate and respond to AFM.

Why is CDC’s case definition not counting all patients with AFM?

• CDC has case definitions for AFM with specific criteria that we use to classify patients as having a confirmed or probable case of this illness. If a patient does not meet these criteria, they are classified as “not a case” of AFM.
• By focusing on patients with the most similar symptoms (confirmed cases), we can better compare them to understand possible risk factors and causes of AFM.
• CDC case classifications do not change treatment or patient care.
• Even though some patients may not meet our case definitions, the information provided about these patients still helps us understand the full spectrum of illness.
• As we continue to learn more about AFM and its initial symptoms, we are working with our partners to refine our case definitions so that we can better understand AFM.

AFM can be caused by viruses, including enteroviruses.

CDC has been tracking AFM since 2014 when the United States recorded the first increase in AFM cases. Two more increases were observed in 2016 and 2018.

These spikes in cases are thought to be caused by enterovirus D68 (EV-D68).

• Most patients developed AFM between August and November.
• At this same time of year, many viruses, including enteroviruses, commonly spread in the U.S.
• Respiratory symptoms and fever from viral infections (such as with enteroviruses) are common, especially in children, and most people recover.
• The increase in 2014 coincided with a national outbreak of severe respiratory illness caused by EV-D68, and increased circulation of EV-D68 was observed in 2016 and 2018.
• EV-D68 was the most common virus detected in specimens from patients with AFM, usually in respiratory specimens.
• AFM patients had antibodies against enteroviruses in their spinal fluid more often than those without AFM. Having antibodies against a virus means that a person was previously infected with that virus.

AFM can also be caused by other viruses, including flaviviruses (West Nile virus, Japanese encephalitis virus), herpesviruses, and adenoviruses.

Most people will have sudden onset of:

• Arm or leg weakness
• Loss of muscle tone and reflexes

Some people will also have:

• Difficulty moving the eyes or drooping eyelids

• Facial droop or weakness

• Difficulty with swallowing or slurred speech

• Pain in arms or legs

• Pain in neck or back

In uncommon cases, people may also have numbness or tingling in arms or legs.

The most severe symptoms of AFM are:

• Respiratory failure (when the muscles involved with breathing become weak and require machines to help patients breathe).
• Serious neurologic complications such as body temperature changes and blood pressure instability that could be life threatening.

Seek Medical Care Right Away

• If you or your child develops any of these symptoms, you should seek medical care right away.
• Clinicians should immediately hospitalize patients since AFM can progress rapidly and require urgent medical care, like assistance with breathing.
• Your clinicians should collect information about your symptoms and send this information to their state or local health departments.

It is important that the tests to help with diagnosis (MRI and laboratory testing of the CSF, respiratory fluid, blood and stool) are done as soon as possible after a patient develops symptoms.

The following tests can be used to help diagnose AFM. A clinician may:

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. Clinicians should consider consulting with specialists in neurology and infectious diseases to assist with the diagnosis of AFM. With the help of testing and examinations, clinicians can distinguish between AFM and other neurologic conditions.

There is no specific treatment for AFM, but a clinician who specializes in diseases like AFM may recommend certain interventions on a case-by-case basis. For example, clinicians may recommend physical or occupational therapy to help with arm or leg weakness caused by AFM. Physical rehabilitation might improve long-term outcomes if implemented during the initial phase of illness.

If your clinician suspects your child has acute flaccid myelitis (AFM), they should hospitalize your child immediately. AFM can progress rapidly and sometimes requires machines to help patients breathe. You can help your child get the best care by taking the following steps:

Help your child get early treatment

Helping your child get early treatment starts by detecting the symptoms early. You as the parent will likely be the first one to detect early symptoms. You should ensure that you seek medical care right away if you see symptoms of AFM in your child. If your clinician suspects your child has AFM, they should hospitalize your child immediately, do a physical exam of the patient, and perform an MRI to review pictures of the spinal cord. Your clinician should consult neurology and infectious disease experts to discuss possible treatments. We don’t have enough information to know if certain treatments may help some patients, but the following treatments have been used:

• Corticosteroids (used to treat inflammation)
• Intravenous immunoglobulin (used to treat immune disorders)
• Therapeutic plasma exchange (used to remove antibodies from blood)

Ask the clinician about your child’s diagnosis

Clinicians diagnose AFM by taking a careful medical history, doing a physical exam of the patient and performing an MRI to review pictures of the spinal cord. Your child’s clinician is the best source of information about their diagnosis of AFM.

Help your child get the best long-term care after they are diagnosed

If your child has AFM, there are some rehabilitation options that may help improve their outcomes. Physical rehabilitation might also improve long-term outcomes if your clinician implements it early in your child’s illness onset. Some patients have also received nerve transfer surgery (used to repair nerve injuries) in hopes of improving long-term outcomes. Talk to your clinician about these options for your child’s long-term care.

Types of clinicians who may be involved

Many different types of clinicians may be involved in your child’s care. Each clinician has an important role in helping your child get better. These include:

• Primary care doctor
• Neurologist (a clinician who specializes in treating brain and spinal cord illnesses)
• Infectious disease clinician
• Physical therapist (a clinician who treats patients using physical methods such as massage, heat treatment, and exercise)
• Occupational therapist (a clinician who treats patients through rehabilitation and performing activities required in daily life)

Consider Joining Support Groups

Navigating the healthcare system and overseeing your child’s recovery can be a tremendously difficult situation and stressful for everyone involved. We encourage you and your family to reach out to others for support and connect with other parents of children who have AFM.

You can also:

• Talk to your child’s school staff to
  • develop an action plan to help your child succeed in school,
  • locate resources they may have to accommodate this illness,
  • find opportunities for your child to interact with peers, and
  • address any concerns you have.
• Educate others involved in your child’s life about AFM, such as school staff, other family members, and your child’s peers. When people know more about this illness, they may be better able to help and accommodate your child.

Get Your Child Involved in Activities with Others

Encourage friends and family to spend time with your child if they feel well enough for visitors. Spending time with others is also an important part of wellbeing and recovery.