Acute Flaccid Myelitis – Beyond the Hype

I'll bet most every pediatrician has seen the media blitz regarding AFM cases. I've been a little disappointed in most coverage by the lay press; they seem to be making this out to be more mysterious than it really is. (I did see one instance of well-balanced coverage in the Atlantic online, which included a quote from my colleague (and boss!) at Children's National, Roberta DeBiasi.)

Here's the scoop without the hype. Shortly after AFM became better recognized in 2014, CDC developed case definitions that were updated in 2017. The case definitions differ depending on whether one is considering reporting a new case or ultimately classifying a case as Probable of Confirmed AFM. Regardless, three criteria are used. First is the presence of acute onset of flaccid limb weakness, i.e. characterized by diminished or absent deep tendon reflexes. The second characteristic is MRI evidence of a spinal cord lesion largely restricted to gray matter and spanning one or more spinal segments. Lastly, the third feature is evidence of CSF pleocytosis (WBC > 5/cubic mm). A confirmed case consists of the first 2 elements, regardless of CSF findings. Upticks in AFM seem to be occurring in even-numbered years: 2014, 2916, and now 2018. Here is the CDC's current (as of October 31) graph of cases:

I guess the mysterious part of all this, as seen by the lay press, is that no one entity has been shown to be the cause of AFM. However, healthcare providers shouldn't be mystified; we know that many different (and common) viruses can cause encephalitis and myelitis. Also, the same virus infecting one individual might cause only mild upper respiratory symptoms or even no symptoms at all, while the same viral strain could cause AFM in a neighbor. Polio is the classic example of this: 95% of wild polio infections are asymptomatic, and the majority of the rest produce only mild symptoms or aseptic meningitis with no sequelae. Paralytic polio represents the tip of the iceberg, no more than 1-2% of all infections. The role of age seems to be different for AFM, where paralytic disease is seen primarily in children, compared to polio which, although causing paralysis in all age groups is more severe in older individuals.

So far, two different enteroviruses, D68 and 71, have been associated in different years with some but by no means all of the cases. It seems likely that AFM is a syndrome that can be triggered by multiple infectious entities.

The role of primary care pediatricians in AFM management is 2-fold. First, PCPs can help explain AFM to worried patients and families. To that end, the CDC has some excellent resources. Second, PCPs should consider AFM in a child presenting with any type of weakness. Weakness, particularly if associated with diminished deep tendon reflexes, should prompt referral for subspecialty care.

Note that AFM is a reportable disease. Generally, this reporting will be the responsibility of the clinician diagnosing the condition, in this case usually at a referral center. Reporting procedures vary by jurisdiction of the patient's residence. DC, Virginia, and Maryland have information and reporting resources available.