Acute Flaccid Myelitis

* Revised 6/6/2022. This information sheet has been reviewed and approved by members of SRNA’s Medical and Scientific Council.

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 grey 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 every other year (2014, 2016, and 2018) across the United States. Non-polio enteroviruses have been implicated as potential causal factors in the development of AFM. Enterovirus D68 and enterovirus A71 have been suspected in many of these cases, although other enteroviruses such as coxsackievirus have been implicated as well. Enterovirus D68 most often causes a respiratory illness and circulates in the United States during the summer and fall every other year, which coincides with the increase of cases of AFM seen every other year. The expected biennial increase of enterovirus D68 and subsequent AFM cases for 2020 did not occur and can likely be attributed to personal protection and prevention measures in place due to the COVID-19 pandemic. While some models predicted a spike of enterovirus circulation and therefore AFM, we did not see a spike in cases in 2021. 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.