What to know about AFM: the rare polio-like illness

Acute flaccid myelitis (AFM) is a rare, polio-like condition that causes weakness and paralysis in the arms or legs. Though outbreaks do occur, there are typically fewer than 50 cases in the United States each year, according to the Centers for Disease Control and Prevention (CDC).

Recognition and early diagnosis of AFM are critical, since 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 AFM in 2014 after noticing an unusual spike in an illness that led to sudden weakness in the limbs. More than 100 cases were recorded in the U.S. between August and December of that year.

Cases spiked again in 2016 and 2018. In 2016, there were 153 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 severity of the 2018 outbreak caused the rare condition to receive more attention.

In recent years, the number of cases has dropped. Between 2020 and 2025, U.S. AFM cases averaged fewer than 30 per year.

More than 90 percent of people diagnosed with AFM are young children. Most have a mild respiratory illness or fever days before developing muscle weakness, suggesting they had a viral infection before they developed AFM.

Signs and symptoms of AFM

Acute flaccid myelitis affects the nervous system. People with AFM develop lesions in the gray matter inside their spinal cord. The most common warning signs are the sudden arm and leg weakness, 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.

Though AFM triggers polio-like symptoms, the CDC points out that confirmed cases of the condition have not been caused by the poliovirus.

Several possible causes

For some people, AFM may be particularly concerning because there are still more questions than answers. It’s unclear what causes AFM and how it can be most effectively treated.

The fact that AFM tends to spike in the late summer and early fall suggests the condition has a seasonal pattern, explains Christopher Ohl, MD, an infectious disease specialist in Winston-Salem, North Carolina.

Though scientists continue to investigate AFM, they have identified several possible causes. Enteroviruses, particularly EV-D68 (a type of virus that causes an illness similar to a cold), are associated with the condition. The mosquito-borne illness West Nile virus and coxsackievirus A16 (hand, foot, and mouth disease) have also been linked to AFM in some people.

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 people 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, Dr. Ohl explains.

While there is not one specific treatment or cure for AFM, healthcare providers 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 1 in 1,000,000 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. Health experts recommend 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.