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What is acute flaccid myelitis (AFM)?

Acute flaccid myelitis (AFM) is a condition that affects the nervous system, usually in young children. AFM affects the motor neurons in the spinal cord or brainstem and can progress rapidly. The most common symptoms are the sudden onset of weakness in the arms and legs. In rare cases, the loss of muscle tone and reflexes can lead to complete paralysis in one or more limbs. If you suspect your child has AFM, contact your doctor.

Since 2014, there has been an increase in AFM cases every year. Most cases occur between August and October and coincide with the seasonal circulation of viruses, including enteroviruses. Enteroviruses, specifically D68 and A71, are possible causes of the condition. Although AFM is often described as polio-like, recent cases of AFM are not caused by the poliovirus.

Girl in blue shirt rides pink bike on sidewalk

Meet Jane

None of her doctors could explain why her arm got weaker and weaker until she couldn't move her hand. Today, she's back on her bike and playing the piano.

Acute Flaccid Myelitis | Symptoms & Causes

What are the symptoms of acute flaccid myelitis (AFM)?

Acute flaccid myelitis causes weakening of the muscles and the body’s reflexes. Symptoms may include:

  • sudden weakness in the arms and legs
  • sudden loss of muscle tone and reflexes
  • neck, back, arm, or leg pain
  • weakness or drooping in the face or eyelids
  • difficulty swallowing, moving the eyes, or urinating
  • slurred speech
  • numbness or tingling (less common)

In some cases, the symptoms are serious, such as weakness in muscles involved in breathing. This may lead to respiratory failure (requiring help from a machine to breathe).

If your child develops any AFM symptoms, it’s important to contact your doctor right away. AFM can have serious long-term health effects and requires immediate medical attention.

What causes acute flaccid myelitis (AFM)?

There is no single cause of acute flaccid myelitis. Most patients with AFM had a respiratory illness or fever that might have been caused by a viral infection before they were diagnosed with AFM. Enteroviruses are common viral infections in children and, in rare cases, can also cause neurologic illness.

It is not currently known why some patients with viral infections develop AFM while others recover. AFM is often compared to polio, which is a viral infection of the motor neurons. However, no recent U.S. cases have been linked to the poliovirus.

Acute Flaccid Myelitis | Diagnosis & Treatments

How is acute flaccid myelitis (AFM) diagnosed?

Acute flaccid myelitis can be difficult to diagnose because it shares symptoms with neurologic conditions like Guillain-Barré syndrome and acute transverse myelitis. To diagnose AFM, your doctor will review your child’s medical history and examine their nervous system. Your child may also need magnetic resonance imaging (MRI) to create two- and three-dimensional images of their brain and spinal cord.

Your doctor may test the fluid around your child’s brain and spine (cerebrospinal fluid) or check the impulses in the nervous system (nerve conduction). It’s important to consult a neurologist and infectious disease doctor when diagnosing AFM.

How is acute flaccid myelitis (AFM) treated?

There is no specific treatment at this time for acute flaccid myelitis. Your child’s doctor may recommend intravenous immunoglobulin (IVIG) or other medications. Your doctor may also recommend surgery to replace the function of the damaged nerves. In nerve transfer surgery, an orthopedic surgeon transfers healthy nerves to take over the function of the nerves damaged by the virus. In tendon transfer surgery, nearby unaffected muscles are moved to take over the muscles that are weak due to the virus.

How we care for acute flaccid myelitis (AFM)

The Neuroimmunology Center at Boston Children’s Hospital is dedicated to the comprehensive care of children and adolescents who are affected by autoimmune disorders of the brain and spinal cord (neuro-immune disorders). Our program works in collaboration with physiatry, endocrinology, psychiatry, and orthopedics.

Boston Children’s Orthopedic Center blends cutting-edge treatments and surgical approaches with prompt, family-centered care. Our specialists in the upper and lower extremities have extensive experience performing nerve transfers, muscle transfers, and other delicate procedures that maintain and restore function so children can lead full, independent lives.

Acute Flaccid Myelitis | Programs & Services