Acute Flaccid Myelitis: Causes and Symptoms

Author: Giselle Robel Giselle Robel
Category: Health

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 are developing symptoms.

If you or your child develops these symptoms, seek immediate medical care. Because symptoms can progress rapidly. Hospitalization is needed and sometimes a ventilator is required for breathing support.

What is acute flaccid myelitis (AFM)?

AFM is an uncommon disease that resembles polio. The disease is one of the nervous system. Muscle tone and responses become weak (flaccid). Although AFM is rare, it can be very serious, even to the point of making breathing difficult.

Before being described in 2014, AFM might have been diagnosed as a type of transverse myelitis. However, one difference between AFM and transverse myelitis has been found by magnetic resonance imaging (MRI) scans. The gray matter of the spinal cord is inflamed in people with AFM.

The number of cases of AFM has been rising. However, the Centers for Disease Control and Prevention predict that less than 1 person per 1 million people per year in the US will develop AFM. So far, most of the reported cases have involved people younger than age 18, but adults can get AFM.


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

  • arm or leg weakness
  • loss of muscle tone
  • and 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 should I call the doctor?

If you or your child have a leg or arm that suddenly gets weak and does not function well, you should call the doctor right away. If you or your child also show any other symptoms (problems of the face, mouth, eyes), call your doctor right away. Difficulty breathing always requires immediate medical attention.


A virus known as enterovirus might be the cause of Acute flaccid myelitis infection. 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.


It might be hard to diagnose AFM because it resembles other neurological conditions.

  • Physical examination and patient history
  • An MRI of the spinal cord and brain
  • Cerebral spinal fluid (CSF) removal and testing
  • Nerve response testing like nerve conduction velocity (nerve speed) tests
  • Muscle response tests like electromyography
  • Tests of bodily fluids like blood or mucus


There are no specific treatments for this. Physical and occupational therapy to restore movement is seen as being very important. Some doctors might recommend treatments, like steroids, antivirals, or immunoglobulin, which have been used to treat transverse myelitis and other neurological conditions. There is, as yet, little evidence that these are effective.

Sometimes, it is possible to transfer nerves from a functioning site to the affected site. These procedures are often best done by surgeons who specialize in hands and upper extremities.

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.

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