Update on acute flaccid myelitis

Acute flaccid myelitis (AFM) is an uncommon but serious condition for which outbreaks have followed a biennial pattern since 2014. With the next surge of AFM cases predicted in 2020, it is important that pediatricians be familiar with its presenting features because early recognition has implications both for the prognosis of the affected child and for enabling research to understand AFM etiology, said Kevin Messacar, MD, at the American Academy of Pediatrics (AAP) 2019 National Conference and Exhibition, October 28, in New Orleans, Louisiana.

In his session titled “Acute flaccid myelitis,” Messacar presented information on AFM epidemiology, diagnosis, prognosis, and management. He also discussed some recent research advances that are providing insight on infectious causative mechanisms for this recently described disease.

Messacar is assistant professor of Pediatrics at the University of Colorado, Denver, a hospitalist, and infectious disease consultant at Children’s Hospital Colorado Anschutz Medical Campus, Aurora. He told attendees that the term AFM was coined in 2014 after groups of children presented with paralysis of the arms, legs, or muscles of the face and throat. In response to reports of these cases, the Centers for Disease Control and Prevention (CDC) established a case definition to both identify cases and quantify their number. According to the CDC, AFM is defined as acute onset of flaccid limb weakness and magnetic resonance imaging (MRI) involvement of predominantly the gray matter of the spinal cord without identified etiology in individuals aged younger than 21 years.

Messacar said that pediatricians should suspect AFM in any child presenting with weakness in the arms or legs, particularly during late summer or early fall, which have been the peak periods for AFM outbreaks. The history provides another clue to diagnosis as most children will have had a recent febrile illness with respiratory or gastrointestinal symptoms, or signs of hand-foot-mouth disease. The features of the prodromal illness and the prognosis of AFM may vary depending on the associated virus, said Messacar.

The most common virus associated with AFM cases that have occurred throughout the country since 2014 has been enterovirus D68 (EV-D68), but in 2018 in Colorado there was a cluster of cases associated with EV-A71. Most children who had an EV-D68 infection had respiratory symptoms, whereas the initial prodromal illness associated with EV-A71 involved hand, foot, and mouth lesions. In addition, whereas the majority of children with EV-D68–associated AFM have persistent weakness, complete recovery was more common with EV-A71–associated cases.

When AFM is suspected, pediatricians should report cases to their state health department and order an MRI of the brain and spinal cord to confirm the diagnosis. Importantly, they should procure samples as soon as possible from the respiratory tract, blood, stool, and spinal fluid and submit the specimens to the CDC.

“It is hoped that prompt collection of samples from children with AFM will enable identification of its etiology. Unfortunately, the delay between the initial febrile illness and onset of AFM symptoms has been a major impediment to determining the underlying cause,” Messacar said.

“Children typically first experience muscle weakness about 5 to 7 days after the prodromal illness that is likely the inciting infection, and so by the time that AFM is suspected, the window of opportunity to identify a potential pathogen may have passed in some cases,” he said.

Early recognition is also the cornerstone for optimizing management of children with AFM, the mainstay of which is supportive care to maintain breathing, nutrition, and hydration.

“Progressive neurologic injury with AFM can occur quickly, sometimes within a matter of hours, with resulting paralysis of the muscles that support breathing and protect the airway, Messacar pointed out. “Consequently, a significant proportion of children with AFM require intubation and ventilation. Early recognition of AFM is critical so that the necessary support is provided in a timely manner.”

Rehabilitation therapies, including physical therapy, occupational therapy, and speech therapy, should be initiated as soon as the patient is clinically stable and maintained as long as needed to assist children in regaining as much function as possible.

“The majority of children with AFM do not have complete recovery and are left with long-term if not permanent weakness or paralysis. Pediatricians have an important role as quarterback for coordinating ongoing rehabilitation and the complicated care of these children,” Messacar said.

COMMENTARY

Acute flaccid myelitis (AFM) has captured national headlines since outbreaks were recognized in the United States in 2014, 2016, and 2018. Similar to poliomyelitis, patients can experience acute onset of flaccid weakness in one or more limbs, and the condition is most common in children.

Whereas the syndrome of flaccid myelitis can be caused by a number of viruses or immune-mediated pathologies, the late-summer outbreaks occurring on alternating years since 2014 are most associated with a specific enterovirus. This has raised a number of scientific questions and public health concerns. With those issues in mind, and because of the current emphasis on early recognition, reporting, and treatment, it is critical for pediatricians to be aware of AFM.

In a session on this topic at the AAP’s 2019 National Conference and Exhibition, Dr. Kevin Messacar discussed a number of important issues. An update on the current epidemiology and clinical presentations of AFM may be particularly valuable for pediatricians considering that early on, the signs of illness may be missed. Reviewing the differential of acute flaccid weakness is critical for pediatricians as patients may rapidly decline neurologically and suffer respiratory difficulties.

Messacar reviewed the data relative to etiology studies, pointing out that the likely cause in the majority of patients is enterovirus D68, which usually causes a mild upper-respiratory syndrome. He noted the prevalence of a prodromal illness in the majority of patients, followed by rapid neurologic decline a week later.

As Dr. Messacar pointed out, early reporting to public health officials and sampling of nasopharyngeal secretions, cerebrospinal fluid, and blood will be critical for CDC-led efforts to confirm the etiology of spinal cord damage. Pediatricians need to be aware of the public health needs and the individual patient needs. Messacar stressed the importance of supportive care, considerations for therapies to limit damage, and the need for early, albeit prolonged, rehabilitation services.

Benjamin M. Greenberg, MD, MHS, is Distinguished Teaching Professor of Neurology and Pediatrics, University of Texas Southwestern, Dallas, Texas.