AFM is a rare but serious condition that affects the nervous system, causing rapid-onset weakness in one or more arms and legs and spinal cord gray matter lesions. The condition has been associated in some instances with long-term disability.
From Jan. 1 to Nov. 2, of 106 patients with acute flaccid limb weakness, 80 cases from 25 states were confirmed as AFM, according to the MMWR, with another six classified as probable. That's three times the number of confirmed cases seen during the same period in 2017, the CDC said.
During a Nov. 13 press briefing, Nancy Messonnier, M.D., director of the CDC's National Center for Immunization and Respiratory Diseases, updated participants on the agency's findings, boosting that case count to 90 confirmed cases of AFM in 27 states from among 252 case reports under investigation. Most AFM cases were identified in children between ages 2 and 8, she noted, and about half were among males, almost all of whom had fever and/or respiratory illness in the three to 10 days before experiencing limb weakness.
In nearly all patients, an upper limb was involved, with about half having only upper limb involvement.
Of the 80 confirmed AFM cases included in the MMWR, Messonnier said the CDC had tested 125 spinal cord fluid, respiratory and stool specimens from 71. About half of the respiratory and stool specimens were positive for enterovirus or rhinovirus, including EVA-71 and EVD-68.
The spinal cord fluid was positive in two cases, she added. One showed evidence of EVA-71, and the other had evidence of EVD-68. One of the cases was in an adult who was on immune-suppressive medication and the other was in a child who had very rapid progression of paralysis.
"It is important to put these two cases in context," Messonnier said. "Since 2014, we have tested spinal cord fluid of most AFM cases, and in only a few have we identified a pathogen. When a pathogen is found in the spinal fluid, it is good evidence that it was the cause of a patient's illness."
Still, she noted, frequently, no pathogens are found in the spinal fluid despite extensive testing.
"This may be because the pathogen has been cleared by the body or it is in hiding in tissues that make it difficult to detect," Messonnier explained. Alternately, the pathogen may trigger an immune response that damages the spinal cord.
"We know that most patients with AFM have fever and/or respiratory symptoms before developing AFM," she added. "However, at this time of year, many children have fever and respiratory symptoms. Most of them do not go on to develop AFM.
"We're trying to figure out what the triggers are that would cause someone to develop AFM."
So far, no deaths among AFM patients have been reported to the CDC this year.
Messonnier went on to explain that the process for confirming new AFM cases can take a week to a few weeks to complete.
"After a doctor suspects a patient has AFM, the doctor sends the patient's medical information and radiological images to their health department," she said. "The health department sends that information to the CDC. And then CDC staff and a network of AFM expert neurologists classify patients and confirm a case."
Undoubtedly, classifying cases is important as CDC researchers work to identify what triggers development of AFM, said Messonnier, and the agency is striving to expedite the process.
"But taking care of the patient is the No. 1 priority for doctors and the health department," she said. "We want doctors to treat their patients and consult medical experts, if necessary, without waiting for the classification results."
The CDC has created a number of clinician resources on AFM, including a frequently asked questions document, case definitions, specimen collection instructions, a data collection form and interim considerations for clinical management of patients.
Moreover, the CDC has funded state health departments in an effort to increase physicians' awareness and ability to identify possible cases of AFM, said Messonnier, and has increased its network of neurologists on hand to assist with and confirm AFM cases.
In addition, she noted, "We're working with health departments to cross-reference their list of AFM cases with their death registry, even from previous years, to see if patients from previous years have died."
The CDC also has established an AFM task force of national experts in multiple disciplines to help develop a comprehensive research agenda to better understand why AFM affects some children and not others.
Finally, said Messonnier, the CDC has worked directly with clinicians to treat AFM patients since 2014 and will continue to do so going forward. The agency plans to update its considerations for clinical management based on direct feedback from physicians who are treating these AFM patients.
"Unfortunately, because we don't yet know the cause of all AFM cases, these considerations are not as specific as we would like," she acknowledged.
As for CDC recommendations for targeted therapies or specific interventions to treat AFM, Messonnier said there still isn't enough evidence to endorse use of any such measures. In the meantime, the agency recommends clinicians expedite neurology and infectious disease consultations to discuss treatment and management considerations.
"As a mom, I know what it's like to be scared for your child, and I understand parents want answers," she said. "The 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."