Cases of acute flaccid myelitis (AFM), a rare, polio-like illness that can cause paralysis, are expected to follow past trends and increase this year, according to the U.S. Centers for Disease Control and Prevention (CDC). As of August 31, 2020, there have been 21 confirmed cases this year.
AFM primarily strikes children ages four to six (about 90% of cases) but can also affect older children and adults, according to the CDC. The illness typically starts with a fever and/or respiratory symptoms. These problems begin about 1 to 2 weeks before muscle weakness suddenly develops in one or more limbs. Other common symptoms include loss of muscle tone, difficulty walking, and pain in the neck, back, legs, and arms. The long-term outcome for people with AFM is unknown. Treatment focuses on managing the symptoms and may include aggressive physical therapy.
Cases of AFM usually peak during August through November. A recent report in the CDC's Morbidity and Mortality Weekly (MMWR) notes that since the agency began tracking AFM in 2014, cases have surged every two years. During the most recent spike in 2018, the CDC received reports of 238 confirmed cases in children in the U.S. More than three-quarters of patients sought medical care within a day of having muscle weakness. Most of them (64%) went directly to an emergency department. Overall, 98% of patients were hospitalized and 54% were admitted to an intensive care unit (ICU). Nearly one-fourth of ICU patients needed intubation and a ventilator to breathe, according to the report.
Published reports say that fewer than 1 in 1 million children worldwide have been affected by AFM. While Canada, France, Britain, Norway and other countries have reported cases, U.S. outbreaks of this devastating illness have been more pronounced. More than 630 Americans have been diagnosed with AFM since the CDC began tracking the disease in 2014.
Scientists are still unsure exactly what causes AFM. According to the National Institutes of Health, evidence from scientific studies increasingly suggest the cause is a type of virus called an enterovirus. The CDC says that the enterovirus EV-D68 in particular is a likely, primary cause of AFM in the U.S. Poliovirus, which is an enterovirus that causes paralysis, has not been linked to AFM, according to the CDC. Some other possible causes of AFM include flaviviruses (e.g., West Nile virus), adenoviruses, and herpes viruses. AFM generally has not been linked to SARS-CoV-2, the virus that causes COVID-19. Coronaviruses are not in the same genetic family as the enteroviruses associated with AFM.
Some of the viruses linked to AFM cause respiratory symptoms and can easily spread between people. The CDC urges people to protect themselves by taking steps to lower the risk of catching respiratory illnesses or spreading them to others. Such steps include washing hands well and often, covering coughs and sneezes with tissues or sleeves, disinfecting surfaces, and avoiding people who are ill.
AFM can be difficult to diagnose because it resembles other diseases affecting the nervous system. When diagnosing AFM, healthcare practitioners rely on collecting a thorough medial history, noting a patient's signs and symptoms, a physical exam, and an MRI of the spine, which may show lesions in the gray matter of the spinal cord. Other tests that check nerve conduction and muscle reflexes may be performed. Laboratory tests may include testing of cerebrospinal fluid, blood, stool and/or respiratory samples to detect viruses believed to cause the disease.
The CDC urges parents, healthcare practitioners, and emergency room staff to be aware of AFM and suspect it when children suffer sudden limb weakness, especially in late summer through early fall. Recent respiratory illness or fever and the presence of neck or back pain or any neurologic symptom such as muscle weakness, loss of muscle tone, or difficulty walking should also spur concern.
"As we head into these critical next months, CDC is taking necessary steps to help clinicians better recognize signs and symptoms of AFM in children," said CDC Director Robert Redfield, M.D. "Recognition and early diagnosis are critical. CDC and public health partners have strengthened early disease detection systems, a vital step toward rapid treatment and rehabilitation for children with AFM."
Some experts are concerned that parents may hesitate to seek care for children suffering AFM symptoms because they are worried about the risks of contracting COVID-19. But CDC officials have emphasized that AFM is a medical emergency and those suffering potentially related symptoms get immediate medical care, even in areas with high rates of COVID-19.
It's unknown how the COVID-19 pandemic and social distancing measures may affect the circulation of viruses that can cause AFM, or if COVID-19 will impact the healthcare system's ability to promptly recognize and respond to AFM, CDC added. If social distancing measures decrease circulation of enteroviruses this year, AFM cases may be fewer than expected or the outbreak may be delayed.
In the meantime, Thomas Clark, M.D., Deputy Director of CDC's Division of Viral Diseases, has called upon healthcare practitioners to be vigilant about AFM and promptly evaluate anyone with its symptoms. He noted that some doctors may need to see patients via telemedicine appointments. Healthcare practitioners should not delay hospitalizing patients with suspected AFM, he emphasized.