Confirmed cases of acute flaccid myelitis (AFM) have risen to 90 while another 162 are under investigation, federal health officials said Tuesday.
The disease, which is characterized by sudden muscle weakness, has been confirmed in 27 states and mostly impacts children.
Centers for Disease Control and Prevention (CDC) officials said they are stepping up their efforts to determine the cause as well as long-term impacts of AFM.
“As a mom, I know what it’s like to be scared for your child and I understand parents want answers,” said Nancy Messonnier, M.D., director of the CDC’s National Center for Immunization and Respiratory Diseases. “CDC is a science-driven agency. Right now, the science doesn’t give us an answer. That’s why we at CDC along with all our partners will keep looking for answers.”
AFM is defined as:
- acute onset of flaccid limb weakness and
- MRI showing spinal cord lesion largely restricted to gray matter spanning one or more vertebral segments (confirmed case) or cerebrospinal fluid with pleocytosis (probable case).
The CDC has seen spikes every other year since 2014. Case counts so far are on par with 2016 and 2014, which saw 149 and 120 confirmed cases respectively.
The CDC released a new Morbidity and Mortality Report Tuesday detailing 80 of the confirmed cases this year. Among those, the median age was 4 years and 59% were male. Most had a fever or respiratory illness in the weeks leading up to their limb weakness. About 47.5% experienced weakness only in their upper limbs and almost 29% had weakness in all four limbs.
Specimen testing on 71 of the patients showed just over half were positive for an enterovirus or rhinovirus, including enterovirus D68 and enterovirus A71. Only two patients had spinal fluid that tested positive for an enterovirus.
“We’re not sure if the reason we’re not finding pathogens in all of these patients is because it’s cleared, is because it’s hiding, is because it’s something we haven’t tested for,” Dr. Messonnier said. “Similarly, even in the patients that we’re finding a pathogen we’re not sure yet if that pathogen is directly the cause of their AFM.”
She said it is possible that a virus is triggering an autoimmune response that in turn leads to limb weakness. The CDC has formed a task force that is investigating a cause for the disease. It also plans to release updated clinical guidance later this week.
Physicians should be vigilant for patients with limb weakness, which also may present with facial droop or difficulty swallowing. They should ask whether patients recently experienced respiratory or gastrointestinal illness. Those who suspect a patient has AFM should perform a workup including MRI, spinal tap and collection of respiratory, stool, serum, and spinal fluid samplesfor testing and report suspected cases to their state or local health department.
Intravenous immunoglobulin, corticosteroids and plasmapheresis have been the most common treatments for AFM, but CDC experts say there is not enough data to support a preference for any of these or a reason to avoid them. Physicians should consult neurology and infectious disease experts.
Patients with AFM have had a variety of outcomes with some making full recoveries and others experiencing long-term difficulties. None of the patients who have contracted the disease this year have died, according to the CDC. However, officials said they plan to follow outcomes more closely as they try to learn more.