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.