Acute flaccid myelitis (AFM) is an uncommon but serious neurologic condition that causes weakness in the arms or legs. If your child develops these symptoms, you should seek medical care right away.

Symptoms of AFM

Less common symptoms of AFM include numbness or tingling in the limbs and neck. A child may also have difficulty breathing because of weakness of muscles that support breathing.

Most children with AFM will have sudden onset of arm or leg weakness.

Some children might have arm, leg, or neck pain before the weakness begins.

AFM diagnosis

A doctor will review a patient’s medical history. They will also carefully examine the nervous system and places of weakness, low muscle tone, and decreased reflexes. Magnetic resonance imaging (MRI), lab testing of the cerebrospinal fluid, and tests to measure how the nerves are working might also be used to diagnose AFM.

Causes of AFM

AFM can be caused by viruses. Since 2014, most of the children with AFM (more than 90%) had a respiratory illness or fever before they developed arm or leg weakness.

Increases in AFM cases happened in 2014, 2016, and 2018, with most cases occurring between August and October. At this same time of year, viruses, including enteroviruses, commonly spread. Data collected since 2014 indicate that enteroviruses, and more specifically enterovirus D68 (EV-D68), play a major role in the recent increases in AFM. Respiratory symptoms and fever from viral infections are common, especially in children, and most people recover. It is unclear why a small number of people develop AFM after having a virus.

AFM is sometimes referred to as a “polio-like” illness. This is because the symptoms look similar to those of polio. However, all the stool specimens from AFM patients tested negative for poliovirus. This means that the cases of AFM in the U.S. since 2014 were not caused by poliovirus.

AFM treatment

There is no specific treatment for AFM, but a doctor who specializes in treating brain and spinal cord illnesses (neurologist) might recommend certain treatments on a case by-case basis. Doctors will also recommend physical and occupational therapy to help with arm or leg weakness.

Clinicians and public health officials who manage the care of individuals with AFM can review AFM Clinical Guidance | CDC.  

AFM is a medical emergency because it can cause problems with breathing. Children who have symptoms of AFM should be seen by a doctor right away.

Prevention

Even though AFM can be caused by viruses, we do not know what triggers AFM in a person, so there is no specific action that could prevent AFM. Most children who developed AFM had a respiratory illness or fever, likely from a viral infection.

How is CDC tracking AFM cases?

Doctors who might have a patient with AFM send medical information and test results to their health departments, who then send this information to CDC’s AFM experts to review. The submitted cases are then classified as confirmed, probable, suspect, or not a case of AFM based on criteria for the AFM case definition. CDC sends the classification back to the health department who shares it with the doctor who then shares it with the patient. The process of case classification can take time to complete because of all the information that needs to be gathered and reviewed. However, this process is meant to track the trends of AFM in the United States over time and should not delay treatment or diagnosis.

This information is not intended to replace advice given to you by your health care provider. Make sure you discuss any questions you have with your health care provider.