Acute flaccid myelitis is an uncommon neurological condition that affects the spinal cord, leading to muscle weakness. It affects infants more commonly than adults.

According to the Centers for Disease Control and Prevention (CDC), more than 90% of cases occur in infants.

Researchers and scientists do not yet understand everything about this condition, but organizations such as the CDC are researching it and trying to get more information.

In this article, we discuss acute flaccid myelitis (AFM) in more detail, including its symptoms and causes, when to see a doctor, and how to treat and manage it.

a doctor examining a girls leg for signs of Acute flaccid myelitisShare on Pinterest
A person with AFM may experience sudden arm or leg weakness.

AFM is a neurological condition.

According to the CDC, it is uncommon, but doctors have been diagnosing more and more people in the United States since 2014.

AFM affects the central nervous system (CNS). The part that it affects most is an area of the spinal cord called gray matter.

Although AFM has some similarities to polio, since 2014, all tests for polio in people with AFM have been negative.

It is important that people seek medical attention immediately if any of the symptoms of AFM appear. The most common symptoms include:

  • sudden arm or leg weakness
  • sudden loss of muscle tone and reflexes
  • drooping eyelids or finding it difficult to move the eyes
  • facial droops
  • difficulty swallowing
  • slurred speech
  • pain in the neck, back, and legs

People may also experience numbness and tingling and find that they are unable to urinate. However, these symptoms are less common.

In very severe cases, AFM may lead to respiratory failure and sudden temperature and blood pressure changes.

Although the cause of AFM remains unknown, the CDC state that they think that viruses, including enteroviruses, play an important role. They note that from 2014, more than 90% of people with AFM had symptoms of a viral infection before they developed AFM.

Enteroviruses are a group of viruses that cause a variety of illnesses that are typically mild, although an enterovirus does cause polio.

Non-polio enteroviruses typically cause 10–15 million infections in the U.S., and most people who contract these viruses either do not become ill or have a mild illness, such as the common cold.

However, non-polio enteroviruses can cause serious illness if they infect the CNS.

According to the Genetic and Rare Diseases Information Center (GARD), although most people develop symptoms of AFM after a viral infection, in some cases, researchers cannot find a link between a virus and the onset of AFM symptoms.

Researchers and scientists do not know how an infection triggers AFM or why some people seem more at risk after a viral infection when others are not.

According to the GARD, there is no specific treatment for AFM. Some treatments that doctors may try include:

  • corticosteroids
  • blood plasma exchange
  • antiviral drugs
  • immunoglobulin treatment

However, a 2016 study found that none of these treatments significantly alleviated the symptoms of AFM.

A small 2017 study focusing on outcome rather than treatment found that all eight of the children with AFM who took part in the study had improved symptoms after a year. However, they still experienced muscle weakness.

Long-term care

The CDC suggest that physical rehabilitation options may improve long-term outcomes. Some people have also undergone nerve transfer surgery to help repair nerve injuries.

Throughout the recovery process, a person may need to see:

  • a primary care doctor
  • a neurologist, who treats spinal cord and brain illnesses
  • a physical therapist
  • an infectious disease doctor
  • an occupational therapist, who helps with rehabilitation and performing daily activities

Doctors may find it difficult to diagnose AFM because its symptoms are very similar to those of other neurological conditions, such as transverse myelitis and Guillain-Barre syndrome.

If they suspect AFM, doctors may:

  • perform a neurological exam
  • take an MRI scan
  • order lab tests on fluids that cushion the brain and spinal cord
  • check that the nerves respond properly

It is important to seek immediate medical advice if any symptoms of AFM appear because it can progress quickly.

A doctor will likely admit the person to the hospital immediately.

According to a 2017 review, researchers are currently unsure of the long-term outlook for people with AFM.

Research into this is in the very early stages, and, so far, it only provides information for the first year after people start experiencing symptoms.

The evidence to date suggests that children with AFM are likely to recover partially after the first year but will still experience muscle weakness after this time.

AFM is an uncommon but serious neurological condition. It primarily affects infants but does also occur in adults.

Researchers do not currently know the cause of AFM, but there is some evidence that viral infections may cause this condition.

There is no specific treatment for AFM. Doctors may try several different treatments to help people feel better, but studies have found that these treatments are not very effective.

Researchers do not know the long-term outlook for people who have AFM. While there is likely to be some improvement after a year, people will continue to experience muscle weakness.