Acute flaccid myelitis (AFM)


Acute flaccid myelitis (AFM) is a rare but serious condition that affects the spinal cord. It can cause sudden weakness in the arms or legs, loss of muscle tone, and loss of reflexes. The condition mainly affects young children.

Most children have a mild respiratory illness or fever caused by a viral infection about one to four weeks before developing symptoms of acute flaccid myelitis.

If you or your child develops symptoms of acute flaccid myelitis, seek immediate medical care. Symptoms can progress rapidly. Hospitalization is needed and sometimes a ventilator is required for breathing support.

Since experts began tracking acute flaccid myelitis following initial clusters in 2014, outbreaks in the United States have occurred in 2016 and 2018. Outbreaks tend to occur between August and November.


The most common signs and symptoms of acute flaccid myelitis include:

  • Sudden arm or leg weakness
  • Sudden loss of muscle tone
  • Sudden loss of reflexes

Other possible signs and symptoms include:

  • Difficulty moving the eyes or drooping eyelids
  • Facial droop or weakness
  • Difficulty with swallowing or slurred speech
  • Pain in the arms, legs, neck or back

Uncommon symptoms might include:

  • Numbness or tingling
  • Inability to pass urine

Severe symptoms involve respiratory failure, due to the muscles involved in breathing becoming weak. It's also possible to experience life-threatening body temperature changes and blood pressure instability.

When to see a doctor

If you or your child has any of the signs or symptoms listed above, seek medical care as soon as possible.


Acute flaccid myelitis might be caused by an infection with a type of virus known as an enterovirus. Respiratory illnesses and fever from enteroviruses are common — especially in children. Most people recover. It's not clear why some people with an enterovirus infection develop acute flaccid myelitis.

In the United States many viruses, including enteroviruses, circulate between August and November. This is when acute flaccid myelitis outbreaks tend to occur.

The symptoms of acute flaccid myelitis can look similar to those of the viral disease polio. But none of the acute flaccid myelitis cases in the United States have been caused by poliovirus.

Risk factors

Acute flaccid myelitis mainly affects young children.


Muscle weakness caused by acute flaccid myelitis can continue for months to years.


There's no specific way to prevent acute flaccid myelitis. However, preventing a viral infection can help reduce the risk of developing acute flaccid myelitis.

Take these steps to help protect yourself or your child from getting or spreading a viral infection:

  • Wash your hands often with soap and water.
  • Avoid touching your face with unwashed hands.
  • Avoid close contact with people who are sick.
  • Clean and disinfect frequently touched surfaces.
  • Cover coughs and sneezes with a tissue or upper shirt sleeve.
  • Keep sick children at home.


To diagnose acute flaccid myelitis, the doctor starts with a thorough medical history and physical exam. The doctor might recommend:

  • Examining the nervous system. The doctor examines the places on the body where you or your child has weakness, poor muscle tone and decreased reflexes.
  • Magnetic resonance imaging (MRI). This imaging test allows the doctor to look at the brain and spinal cord.
  • Lab tests. The doctor might take samples of the fluid around the brain and spinal cord (cerebrospinal fluid), respiratory fluid, blood, and stool for lab testing.
  • A nerve check. This test can check how fast an electrical impulse moves through the nerves and the response of muscles to messages from the nerves.

Acute flaccid myelitis can be hard to diagnose because it shares many of the same symptoms as other neurological diseases, such as Guillain-Barre syndrome. These tests can help distinguish acute flaccid myelitis from other conditions.


Currently, there is no specific treatment for acute flaccid myelitis. Treatment is aimed at managing symptoms.

A doctor who specializes in treating brain and spinal cord illnesses (neurologist) might recommend physical or occupational therapy to help with arm or leg weakness. If physical therapy is started during the initial phase of the illness, it might improve long-term recovery.

The doctor might also recommend treatment with immunoglobulin that contains healthy antibodies from healthy donors, drugs that lower inflammation in the body (corticosteroids) or antiviral drugs. Or the doctor might recommend a treatment that removes and replaces blood plasma (plasma exchange). However, it's not clear whether these treatments have any benefits.

Sometimes nerve and muscle transfer surgeries are done to improve limb function.

Preparing for an appointment

If you have symptoms of acute flaccid myelitis, seek immediate medical care.

Here's some information to help you get ready for your appointment.

What you can do

Make a list of the following:

  • Signs and symptoms, including any that seem unrelated to the reason for the appointment
  • Any medications, including vitamins, herbs and over-the-counter medicines that you or your child is taking, and their dosages
  • Key personal information, including recent illnesses, travel and activities
  • Questions to ask the doctor

For acute flaccid myelitis, some basic questions to ask the doctor include:

  • Will additional tests be needed?
  • What are the treatment options?
  • What are the benefits and risks of each treatment?
  • Is there one treatment you feel is best?
  • Should additional specialists be seen? What will that cost, and will my insurance cover it?
  • Are there brochures or other printed material that I can have? What websites do you recommend?

Don't hesitate to ask other questions that occur to you.

What to expect from your doctor

The doctor is likely to ask you or your child several questions. Be ready to answer them to allow time later to cover other points you want to address. The doctor may ask, for example:

  • When did you or your child first begin experiencing symptoms?
  • Are the symptoms continuous or occasional?
  • How severe are the symptoms?
  • What, if anything, seems to improve the symptoms?
  • What, if anything, appears to worsen the symptoms?
  • Did you or your child have a viral infection in the past month?

Last Updated Nov 9, 2021

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