Acute Flaccid Myelitis: Something Old and Something New

Abstract

Since 2014, acute flaccid myelitis (AFM), a long-recognized condition associated with polioviruses, nonpolio enteroviruses, and various other viral and nonviral causes, has been reemerging globally in epidemic form. This unanticipated reemergence is ironic, given that polioviruses, once the major causes of AFM, are now at the very threshold of global eradication and cannot therefore explain any aspect of AFM reemergence. Instead, the new AFM epidemic has been temporally associated with reemergences of nonpolio enteroviruses such as EV-D68, until recently thought to be an obscure virus of extremely low endemicity. This perspective reviews the enigmatic epidemiologic, virologic, and diagnostic aspects of epidemic AFM reemergence; examines current options for clinical management; discusses future research needs; and suggests that the AFM epidemic offers important clues to mechanisms of viral disease emergence.

Keywords: acute flaccid myelitis; emerging diseases; enterovirus; neurology.

FIG 1

Epidemic curve of 551 confirmed cases of AFM reported to the U.S. Centers for Disease Control and Prevention by month of onset, 14 August 2014 to 31 January 2019 (6). The epidemic curves of summer/fall AFM correspond closely to typical seasonal peaks of most NPEVs, including EV-D68 (7, 8). Note that the U.S. epidemics have occurred in 2-year cycles, with peak case onsets in the middle week of September in 2014, 2016, and 2018 but with few cases during any season of the intervening years 2015 and 2017.