What is the definition of Acute Flaccid Myelitis?

Acute flaccid myelitis (AFM) is a condition that affects the spinal cord leading to muscle weakness and loss of reflexes. Most people who develop AFM have had a viral illness with flu-like symptoms one to four weeks before symptoms of AFM. Symptoms of AFM include sudden onset (acute) of weakness in the arm(s) or leg(s), loss of muscle tone, and decreased or absent reflexes. Other symptoms may include pain, facial weakness, and difficulty swallowing, speaking, or moving the eyes. It is not clear why some people develop AFM and others do not. Diagnosis is based on the symptoms, a clinical exam, an MRI of the spine, and other laboratory testing. Most people with AFM continue to have muscle weakness for months to years. Sometimes the muscles involved with breathing become weakened, and ventilator support is necessary to help with breathing. The long-term outcome for people with AFM is unknown. Treatment is focused on managing the symptoms and includes aggressive physical therapy.

What are the causes for Acute Flaccid Myelitis?

The cause of acute flaccid myelitis (AFM) is still unclear. Increasing evidence suggests that a type of virus known as an enterovirus is involved. Most people who get sick from an enterovirus get flu-like symptoms such as fever, cough, congestion, vomiting, and/or diarrhea.  Only some of those people who get will develop AFM. It is not clear why some people who get a viral illness get AFM and it is not known how the infection triggers AFM. 
There is no known way to prevent AFM. However, preventing a viral infection can help reduce the risk of developing AFM. Steps to preventing a viral illness include frequent hand washing, cleaning surfaces, avoiding sick people, and staying home when you are sick.

What are the symptoms for Acute Flaccid Myelitis?

The following list includes the most common signs and symptoms in people with acute flaccid myelitis (AFM). These features may be different from person to person. Some people may have more symptoms than others and symptoms can range from mild to severe. This list does not include every symptom or feature that has been described in AFM.

Symptoms may include:
  • Sudden onset of muscle weakness, usually in an arm or leg
  • Pain
  • Facial weakness
  • Difficulty breathing, swallowing, speaking
  • Bowel or bladder control problems
Symptoms usually occur one to four weeks after a flu-like illness (fever, cough, stomach distress). Children are more likely to be affected than adults. Muscle weakness comes on quickly and may involve one to four limbs. The arms are more likely to be affected. Sometimes the muscles involved with breathing become weak and mechanical breathing support (a ventilator) is needed.  Most people who get AFM will have symptoms for months or even years. Because AFM has only recently been described, not much is known about the long-term affects of this condition.

What are the current treatments for Acute Flaccid Myelitis?

There is no specific treatment for acute flaccid myelitis. Aggressive physical therapy may help recovery. Other treatments that have been tried include immunoglobulins, corticosteroids, plasma exchange, and antiviral therapy, but there is no clear evidence that any of these treatments changes the outcome. 

For more detailed information about acute flaccid myelitis, visit the Centers for Disease Control and Prevention (CDC) webpage.

How is Acute Flaccid Myelitis diagnosed?

The Centers for Disease Control and Prevention (CDC) has developed guidance for recognizing acute flaccid myelitis (AFM). Diagnosis is based on recognizing the symptoms. It may include a physical exam, an MRI of the spine, testing of the cerebral spinal fluid (CSF), and tests checking nerve speed (nerve conduction velocity; NCV) and the response of muscles to the messages from the nerves (electromyography; EMG).

AFM can be difficult to diagnose because the symptoms are similar to other neurological diseases, such as Guillain-Barre syndrome (GBS), acute disseminated encephalomyelitis (ADEM), and transverse myelitis. These conditions may need to be excluded before the diagnosis of AFM can be made.