Acute Flaccid Myelitis (AFM) is a type of inflammation in the spinal cord that has specific clinical and MRI features. AFM abnormalities noted on MRI are predominantly found in the gray matter (lower motor neuron) of the spinal cord.
In 2012, an outbreak of AFM occurred in California and more cases were reported in the summer and fall of 2014, 2016, and 2018 across the United States. Non-polio enteroviruses have been implicated as potential causal factors in the development of AFM. The enterovirus D68 and enterovirus A71 have been suspect in many of these cases, although others such as coxsackie viruses have been implicated as well. Enterovirus D68 most often causes a respiratory illness and has been circulating in the United States during the summer and fall every two years since 2014, which coincides with the increase of cases of AFM seen every other year.
It has not been definitively proven that these particular viruses have directly caused cases of AFM but the temporal onset of neurological symptoms with infections produced by those viruses implicate them as direct or indirect triggers of the neurological problem.
AFM
Epidemiology
There are no conclusive studies that identify the actual numbers of individuals specifically affected by AFM, but from 2014 to 2018, the CDC confirmed over 500 reports of those affected by AFM. Not all cases are reported to the CDC nor confirmed by the CDC, so this number is likely an underestimation. There have been reports of AFM in both children and adults, but AFM cases primarily affect children under the age of 18.
Until the recent characterization of AFM in 2014, it is likely that many individuals with initial presentation of flaccid limb weakness and/or paralysis have been diagnosed as having transverse myelitis or Guillain Barre Syndrome in previous years.
