What Causes Acute Flaccid Myelitis (AFM)?

Medically Reviewed on 2/6/2023

Illustration of the brain and spinal cord
Acute flaccid myelitis (AFM) is caused by an enterovirus, which is a common cold and flu virus. AFM can affect the spinal cord and cause muscle weakness.

Acute flaccid myelitis (AFM) is commonly caused by a type of virus called an enterovirus. It is the same virus that causes the common cold and flu. Most people with an enterovirus infection may recover from the disease, but for some, it may progress to AFM.

Other viruses that can cause AFM include

These viruses most often spread during the period between August to November. Children may initially experience fever and respiratory symptoms from viral infections, but most kids get better on their own. The virus, however, may develop in some kids and lead to AFM symptoms.

How quickly does acute flaccid myelitis progress?

Acute flaccid myelitis (AFM) initially starts with a fever. After one to two weeks, AFM may progress to muscle weakness, which may progress rapidly within hours to a few days

The most common symptoms of AFM include

  • Sudden onset of arm or leg weakness
  • Loss of muscle tone
  • Loss of reflexes

Other symptoms of AFM that are not so common may include

  • Difficulty moving the eyes or eyelids
  • Facial droop or weakness
  • Pain in the arms or legs
  • Pain in the neck or back
  • Difficulty swallowing
  • Slurred speech

The most severe symptoms of AFM include

  • Respiratory failure (when the breathing muscles become weak, requiring the assistance of ventilators for breathing support)
  • Serious neurologic complications such as changes in body temperature and blood pressure fluctuations could be life-threatening

Seek immediate medical attention as soon as you see symptoms of weakness in the children as the symptoms tend to progress rapidly, leading to serious complications.

Is acute flaccid myelitis curable?

To date, no specific treatment can cure acute flaccid myelitis (AFM). Early treatment may include supportive care and rehabilitation therapies. Supportive care may include

  • Hospital admissions to prevent the rapid progression of symptoms
  • Intravenous immunoglobulins are given over four to five days if AFM is restricted to grey matter (immunoglobulins lower inflammation in the body)
  • A combination of steroids and plasma exchange if the AFM has spread to upper and lower nerve cells
  • Antiviral drugs to treat the viral infection

However, there is insufficient evidence about the effectiveness of this supportive care in the management of AFM.

Rehabilitation therapy may include

  • Physical or occupational therapy to help recover arm or leg weakness
  • Electrical stimulation

Surgery is the last resort if the muscle movement is not restored with supportive care and rehabilitation therapy. Nerve transfer is a surgical procedure that involves connecting a working nerve to a dysfunctional muscle. Over time, the nerve grows into a muscle, then becomes a functional muscle. It helps children get better movement and strength in their limbs.

Is acute flaccid myelitis reversible?

It is still unknown if acute flaccid myelitis (AFM) can be reversed completely. Most studies have reported that children with AFM may regain some strength over time. But many children may still face muscle weakness in the affected limb for months or years. Recovery is still possible with rehabilitation therapy but may be gradual and requires patience.


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Medically Reviewed on 2/6/2023
Image source: iStock Images

Acute flaccid myelitis: https://www.uptodate.com/contents/acute-flaccid-myelitis#H1124275665

Acute Flaccid Myelitis: https://medlineplus.gov/acuteflaccidmyelitis.html

Acute flaccid myelitis: cause, diagnosis, and management: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7909727/

Acute flaccid myelitis (AFM): https://www.mayoclinic.org/diseases-conditions/acute-flaccid-myelitis/diagnosis-treatment/drc-20493060

Causes of Acute Flaccid Myelitis (AFM): https://www.cdc.gov/acute-flaccid-myelitis/causes.html