Updated on September 26, 2024.
In 2023, there were 18 confirmed cases of acute flaccid myelitis (AFM) in the United States out of 40 that were under investigation, according to the Centers for Disease Control and Prevention (CDC).
AFM causes weakness and paralysis in the arms or legs. As health officials learn more about this rare, polio-like condition, they've asked doctors to be vigilant and promptly report all suspected AFM cases to their local health departments.
Recognition and early diagnosis are critical. The condition can progress rapidly over the course of hours or days, leading to more serious complications that require urgent medical care, such as help with breathing. Prompt treatment is critical for better outcomes, the CDC cautions.
Most cases involve children
Health officials began monitoring the condition back in 2014 after noticing an unusual spike in an illness that caused sudden weakness in the arms and legs. As of September 2024, there have been more than 750 confirmed cases.
Similar to 2014, cases spiked in 2016 and 2018. In 2016, there were 153 total confirmed cases in 39 states and the District of Columbia. A total of 238 people in 42 states were diagnosed with AFM in 2018—the highest number of confirmed cases since the CDC began tracking the condition in 2014. The severity of the 2018 outbreak caused the rare condition to receive even more attention. In more recent years, the number of cases has dropped.
Most of the people diagnosed with AFM are children. In fact, more than 90 percent of those diagnosed with AFM in 2018 were kids with a median age of about 5 years old. More than 90 percent of these patients also had a mild respiratory illness or fever, suggesting they had a viral infection before they developed AFM, the CDC reports.
The seemingly mysterious illness captured headlines, fueled concerns among parents and prompted federal health officials to issue warnings about the condition. But what exactly is AFM and how worried should you be?
What is it?
Acute flaccid myelitis is a serious condition that affects the nervous system. People with AFM develop lesions in the gray matter inside their spinal cord. The most common warning signs are sudden weakness in the arms or legs as well as loss of muscle tone and loss of reflexes.
Additional symptoms of AFM may include:
- Droopy face or eyelids
- Trouble moving the eyes
- Difficulty swallowing
- Slurred speech
- Trouble breathing
- Pain in the arms, legs, neck or back
In extreme cases, AFM may cause paralysis. Despite the fact that AFM triggers polio-like symptoms, the CDC points out the confirmed cases of the condition were not caused by the poliovirus.
Searching for clues
For some people, AFM may be particularly concerning because there are still more questions than answers. It’s unclear why AFM appears to be on the rise, what causes it and how it can be most effectively treated.
Back in 2014, there was an outbreak of respiratory illness among kids, many of whom had asthma and other lung disease. This outbreak was caused by an enterovirus, known as EV-D68, which was linked with AFM, explains Christopher Ohl, MD, an infectious disease specialist at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina. As a result, the CDC began monitoring the condition and testing samples of patients’ spinal fluid and blood for evidence of what might be causing the illness. This ongoing investigation could help explain the increasing prevalence of AFM.
“There is a high level of scrutiny and if you’re looking for something, you’re going to find more,” Dr. Ohl says.
Several possible causes
The fact that AFM tends to spike in the late summer and early fall suggests the condition has a seasonal pattern, Ohl adds. The annual resurgence of the condition was also less notable in 2015 and 2017 than it was in 2014 and 2016. Then, cases hit a new high in 2018.
Enteroviruses, particularly EV-D68 (a type of virus that causes an illness similar to a cold) and EV-A71 (one of many non-polio enteroviruses) are likely responsible for these peaks in cases, according to the CDC.
Scientists investigating AFM, however, have identified several possible causes, including toxins in the environment and certain viral infections, such as the mosquito-borne illness, West Nile virus. Coxsackievirus A16 (hand, foot and mouth disease) has also been pinpointed as a possible trigger in some patients.
Health officials still haven’t found one clear common link among all AFM cases that fully explains the increasing incidence of the condition. This likely means that there is more than one cause, Ohl says.
How AFM is diagnosed and treated
The warning signs of AFM may be confused with other neurological disorders, such as Guillain-Barre syndrome (GBS), a condition that causes the immune system to attack part of the nervous system.
A neurological exam and an MRI of the brain and spinal cord are needed to confirm an AFM diagnosis. Some patients may also undergo a spinal tap, which is a procedure that involves checking the cerebrospinal fluid for potential pathogens.
The large variety of treatments that have been used to manage AFM—including antiviral and anti-inflammatory drugs as well as drugs to suppress patients’ immune system response—have not been effective. Unlike other parts of the body, which may heal more readily, damaged nerve tissues take much longer to recover, Ohl explains.
While there is not one specific treatment or cure for AFM, doctors may recommend certain therapies for individual patients, including physical or occupational therapy to help them regain mobility or strengthen their arms or legs.
Some AFM patients may face lingering effects for months or even years, but a full or nearly full recovery over time is possible, he says. Scientists are still trying to figure out why some people recover more fully and quickly than others. Some patients may be genetically more susceptible to the condition, Ohl points out.
Should you be worried?
It’s important to remember that AFM is still very uncommon.
“It’s really, really rare,” Ohl says. “It’s sort of like winning the lottery—not very likely.”
In the U.S., it’s estimated that fewer than one in a million people will develop the illness each year. By way of comparison, Ohl points out that there are more deaths, hospitalizations, and long-term effects from the flu each year than from AFM.
What can you do to prevent AFM?
AFM is still under investigation but there are some general things you can do to help protect against the viral infections that have been linked to the condition. The CDC recommends taking the following precautions:
- Make sure you and your children are up to date on your vaccines.
- Practice good hand hygiene, washing often with soap and water for at least 20 seconds.
- Don’t touch your face with unwashed hands.
- Avoid close contact with people who are sick.
- Clean and disinfect commonly touched surfaces, such as doorknobs and toys.
- Cover coughs and sneezes with a clean tissue or upper shirt sleeve—not hands.
- If you notice anyone, particularly a child, experiencing sudden weakness or other symptoms of AFM, you should seek medical attention right away.
The CDC provides more information on its ongoing AFM investigation.
