Overview

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. Another outbreak is expected in 2020. Outbreaks tend to occur between August and November.

Symptoms

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.

Causes

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.

Complications

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

Prevention

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.

Sept. 22, 2020
  1. About acute flaccid myelitis. Centers for Disease Control and Prevention. https://www.cdc.gov/acute-flaccid-myelitis/about-afm.html. Accessed Aug. 7, 2020.
  2. Acute flaccid myelitis. Genetics and Rare Diseases Information Center. https://rarediseases.info.nih.gov/diseases/13142/acute-flaccid-myelitis. Accessed Aug. 7, 2020.
  3. Fatemi Y. Acute flaccid myelitis: A clinical overview for 2019. Mayo Clinic Proceedings. 2019; doi:10.1016/j.mayocp.2019.03.011.
  4. Helfferich J, et al. Acute flaccid myelitis and enterovirus D68: Lessons from the past and present. European Journal of Pediatrics. 2019; doi:10.1007/s00431-019-03435-3.
  5. Greenberg B. Acute flaccid myelitis. https://www.uptodate.com/content/search. Accessed Aug. 7, 2020.
  6. Kidd S, et al. Vital signs: Clinical characteristics of patients with confirmed acute flaccid myelitis, United States, 2018. MMWR Morbidity and Mortality Weekly Report. 2020; doi:10.15585/mmwr.mm6931e3.

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Acute flaccid myelitis (AFM)