Acute Flaccid Myelitis

Acute flaccid myelitis (AFM) is a rare neurological condition that causes your muscles and reflexes to become weak. It often affects your upper limbs and can affect the muscles you need to breathe as well. Because of this, it’s important to seek medical care as soon as possible if you or your child develop symptoms.


What is acute flaccid myelitis?

Acute flaccid myelitis (AFM) is a rare and serious neurological condition that causes certain muscles and reflexes to become weak (flaccid). The symptoms come on suddenly and can also affect your ability to breathe.

AFM causes inflammation in the gray matter of your spinal cord. You have grey matter in your brain and spinal cord (central nervous system). Of all the types of central nervous system tissue, it plays the most significant part in allowing you to function normally. Gray matter in your spinal cord specifically plays a role in controlling movement.

AFM is a relatively new diagnosis — researchers first described it in 2014. Previously, healthcare providers and researchers thought it was a type of transverse myelitis.


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What is the difference between acute flaccid myelitis and Guillain-Barré syndrome?

Acute flaccid myelitis and Guillain-Barré syndrome (GBS) are both rare neurological conditions that cause muscle weakness, but they’re different.

In GBS, your body has an autoimmune response that damages peripheral nerves — the nerves that connect your central nervous system (brain and spinal cord) to your limbs and organs. AFM affects the gray matter of your spinal cord.

The muscle weakness in GBS usually begins in your feet and legs and travels up your body. In AFM, muscle weakness can begin in your legs or arms.

Another difference is that AFM typically affects children, whereas GBS most commonly affects adults aged 40 or older.

Who does AFM affect?

About 90% of acute flaccid myelitis cases affect young children between the ages of 1 and 7, but adults can get AFM, too.


How common is acute flaccid myelitis?

Acute flaccid myelitis is rare. Researchers estimate that fewer than 1 person per 1 million people per year in the U.S. develop AFM. However, the number of cases has been rising.

Cases have usually occurred in clusters in certain geographical areas with a distinct seasonal biennial pattern (every other year). For example, there was a cluster of cases in California in 2012 and a cluster in Colorado in 2014.

Symptoms and Causes

What are the symptoms of acute flaccid myelitis?

Symptoms of acute flaccid myelitis include the sudden onset of:

  • Arm or leg weakness.
  • Loss of muscle tone.
  • Loss of reflexes (areflexia).
  • Loss of coordination and balance.

These symptoms develop over a few hours or days.

Other symptoms include:

AFM can affect any or all of your limbs, but it most commonly affects your upper limbs.

Sometimes, AFM can affect the muscles you need to breathe. This can lead to respiratory failure, which is life-threatening and requires immediate treatment.

Signs of respiratory failure include:

  • Rapid and shallow breathing.
  • Extreme fatigue and sleepiness.
  • Restlessness.

If you or your child develop any symptoms of AFM, seek medical care right away.


What causes acute flaccid myelitis?

Researchers don’t know the exact cause of acute flaccid myelitis, but they think that viruses, especially non-polio enteroviruses, play a role in causing the condition. Most people with AFM had a mild respiratory illness (such as the common cold) or fever before they developed AFM.

Researchers and healthcare providers have suspected enterovirus D68 and enterovirus A71 in many AFM cases. Enterovirus D68 most often causes a respiratory illness and circulates in the United States during the summer and fall every other year.

Diagnosis and Tests

How is acute flaccid myelitis diagnosed?

It can be difficult for healthcare providers to diagnose AFM, as it’s rare and resembles other neurological conditions, such as transverse myelitis, Guillain-Barré syndrome and polio.

Your provider will ask about your symptoms and medical history. They’ll likely perform or order several tests to help diagnose AFM and/or rule out other conditions. Tests include:

  • Physical exam.
  • Neurological exam.
  • MRI of your spinal cord and brain to look for changes in the gray matter of your spinal cord. This is the most useful test for confirming AFM.
  • Spinal tap to check cerebral spinal fluid (CSF) to look for signs of inflammation.
  • Nerve response tests like nerve conduction studies.
  • Muscle response tests like electromyography.

Management and Treatment

What is the treatment for acute flaccid myelitis?

There’s no cure or specific treatment for acute flaccid myelitis. Instead, managing symptoms is the goal. If possible, it’s best to see a neurologist who has experience in treating and researching AFM.

Physical therapy and occupational therapy can help with arm and/or leg weakness. Neurologists typically recommend other treatments on a case-by-case basis. For example, peripheral nerve surgery that prevents muscle atrophy has been effective in some people with AFM.

As AFM is a rare and relatively new diagnosis, scientists and providers still have a lot to learn about it and its treatment.


Can I prevent acute flaccid myelitis?

As researchers don’t know what specifically triggers acute flaccid myelitis, there’s no known way to prevent it.

Viruses, including enteroviruses, can lead to AFM. There are steps you can take to lower your risk of getting sick from a virus, including:

  • Wash your hands often with soap and water, including before and after eating, after using the bathroom, after touching an animal and after taking care of someone who is sick.
  • Avoid touching your face with unwashed hands.
  • Avoid close contact with people who are sick.
  • Stay up to date on recommended vaccinations.
  • Clean and disinfect surfaces that you frequently touch.

Outlook / Prognosis

What is the prognosis for acute flaccid myelitis?

As acute flaccid myelitis is a newly recognized condition, researchers don’t yet know the long-term prognosis (outlook) for people with the condition.

Most people continue to improve over time with ongoing physical therapy. Less than 10% of people with AFM recover completely.

What are the possible complications of acute flaccid myelitis?

AFM can affect the muscles you need to breathe properly. This can result in respiratory failure, which is a medical emergency. People with respiratory failure require machines to help them breathe. About a third of people with AFM require intubation and ventilation.

AFM can also cause serious neurologic complications, such as body temperature changes, blood pressure instability and irregular heart rate, which can be life-threatening.

Get medical care as soon as possible if you or your child experience these symptoms.

Living With

When should I see my healthcare provider?

If you or your child have sudden muscle weakness in one or more limbs, seek medical care as soon as possible. AFM can progress quickly and lead to issues with breathing.

If you or your child have a diagnosis of AFM, you’ll need to see your healthcare team regularly to receive treatment, such as physical therapy, and to monitor your symptoms.

A note from Cleveland Clinic

It’s important to seek immediate medical care if you or your child have sudden muscle weakness. Researchers and healthcare providers are still learning about acute flaccid myelitis (AFM), but know that they’ll carefully monitor your symptoms and suggest treatments to manage them.

Medically Reviewed

Last reviewed on 11/29/2022.

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