Acute Flaccid Myelitis (AFM) vs.Polio

Medically Reviewed by Sabrina Felson, MD on March 03, 2023

Polio and acute flaccid myelitis (AFM) are illnesses that cause muscle weakness and paralysis (when you’re not able to move). They both typically affect children.

Polio is a viral infection that paralyzed more than 15,000 people in the U.S. each year -- mostly children -- in the early 1950s. It’s been wiped out in this country thanks to a vaccine, but there are still some cases reported in places, including Pakistan and Afghanistan.

The suspected cause of modern AFM is something called enterovirus D68 which occurs in the gastrointestinal tract but it is )unclear how the virus triggers it.)

AFM causes sudden weakness in your arms and legs, along with a loss of muscle tone and sometimes pain. Your face may also feel weak. These symptoms are usually preceded by a runny nose, cough, congestion, or fever in the days to weeks before the onset of weakness.

Other symptoms of AFM include:

  • Drooping eyelids and trouble moving your eyes
  • A hard time swallowing or speaking
  • Slurred speech
  • Trouble breathing

With polio, most children who have the virus don't show any signs of it. Only about 1 in 4 kids who are infected have symptoms like these:

These typically last 2 to 5 days, then go away.

A much smaller number of children who get the virus have more serious symptoms like:

  • A pins-and-needles feeling in their legs
  • A hard time moving their arms and legs
  • Trouble breathing

Only about 1 out of every 200 children with the virus has paralysis, but when it happens, it can be permanent.

Doctors diagnose polio with a physical exam, a swab of your throat, and a stool sample. Your doctor also might take a sample of your blood and spinal cord fluid. These are sent to a lab, where technicians check for the poliovirus. 

AFM is harder to diagnose because its symptoms can be a lot like those of other diseases related to your brain and nervous system, such as transverse myelitis and Guillain-Barre syndrome.

Doctors do the following to try to find out if it’s AFM or something else:

  • Check your muscle tone and reflexes with a physical exam
  • Get a closer look at your brain and spinal cord with an MRI scan; this uses radio waves and powerful magnets to make detailed images of the inside of your body.
  • Test the fluid around your brain and spinal cord; this is called a spinal tap or lumbar puncture.
  • See how well your nerves respond to electrical impulses

There’s no cure for either polio or AFM and treatment is supportive, ideally allowing your body to recover. Children with either polio or AFM may need:

  • Pain relievers like ibuprofen to ease pain and bring down fever
  • Fluids to keep them from being dehydrated
  • A machine called a ventilator to help them breathe
  • Physical therapy to make weak muscles stronger
  • Occupational therapy to help with everyday activities like dressing and eating

Most of the time, polio is asymptomatic and goes away within a few days.  Between 4-8% of patients experience mild symptoms, lasting only a few days. Less than 2% experience sever poli. Even children who have the most serious kind are rarely paralyzed.

But a small number of people can have symptoms like these years afterward:

Doctors don't know the long-term outlook for AFM. Some people get better and don’t have any lingering effects, while others have weak muscles for a long time afterward.

The polio vaccine will help keep your child from getting the virus that causes the disease. Children need four doses of the vaccine at ages:

  • 2 months
  • 4 months
  • 6 to 18 months
  • 4 to 6 years

There’s no vaccine for AFM and no sure way to prevent it. But you can lower your child’s chances of getting a virus that might trigger it by teaching your children to wash their hands often with soap and water or to use hand sanitizer.