Acute Flaccid Myelitis (AFM)

Acute flaccid myelitis is a rare but serious neurological condition that affects the spinal cord. It leads to sudden weakness in one or more arms or legs, along with reduced muscle tone and loss of reflexes. The condition occurs most often in young children, though adults can be affected in rare cases.

In many instances, children experience a mild respiratory illness or fever caused by a viral infection one to four weeks before symptoms of acute flaccid myelitis appear. Once symptoms begin, they can worsen quickly. Because of the risk of rapid progression, immediate medical care is critical. Hospital treatment is usually required, and some patients may need breathing support with a ventilator.

Since health authorities began monitoring acute flaccid myelitis more closely after clusters appeared in 2014, outbreaks have been reported periodically, particularly in late summer and fall. In the United States, cases tend to increase between August and November.

Symptoms

Symptoms of acute flaccid myelitis usually begin suddenly and can progress over hours or days. The most common symptoms include:

• Sudden weakness in one or more arms or legs

• Sudden loss of muscle tone

• Sudden loss of reflexes

Other symptoms may also occur, depending on which nerves are affected. These can include difficulty moving the eyes, drooping eyelids, facial weakness, trouble swallowing, or slurred speech. Some people experience pain in the arms, legs, neck, or back.

Less common symptoms include numbness or tingling and difficulty passing urine. In severe cases, the muscles that control breathing become weak, leading to respiratory failure. Some individuals may also experience dangerous changes in body temperature regulation or unstable blood pressure.

Causes

The exact cause of acute flaccid myelitis is not fully understood. Experts believe it is often triggered by a viral infection, most commonly from a group of viruses called enteroviruses. These viruses frequently cause respiratory illnesses and fever, especially in children, and most infected people recover without complications.

It remains unclear why only a small number of people develop acute flaccid myelitis after a viral infection. In the United States, many viruses circulate seasonally, particularly from late summer through fall, which aligns with the timing of most reported outbreaks.

Although the symptoms may resemble those of polio, cases of acute flaccid myelitis in the United States have not been caused by the poliovirus.

Risk factors

Acute flaccid myelitis primarily affects young children. At this time, no specific genetic, environmental, or lifestyle risk factors have been clearly identified beyond age and recent viral illness.

Complications

The muscle weakness caused by acute flaccid myelitis can be long lasting. In some people, weakness improves over time, but recovery may take months or even years. Others may have persistent weakness or paralysis.

Severe cases can lead to breathing problems that require long-term ventilator support. Ongoing physical therapy and rehabilitation are often needed to help regain strength and improve function.

Prevention

There is no specific way to prevent acute flaccid myelitis. However, reducing the risk of viral infections may lower the chance of developing the condition.

Steps that can help reduce the spread of viral infections include:

• Washing hands frequently with soap and water

• Avoiding touching the face with unwashed hands

• Avoiding close contact with people who are sick

• Cleaning and disinfecting frequently touched surfaces

• Covering coughs and sneezes with a tissue or the upper sleeve

• Keeping sick children at home until they recover

Practicing good hygiene and infection prevention measures is especially important during the late summer and fall months, when cases are more likely to occur.