An outbreak of paralysis among children in the US
Since 2012, American pediatric ICU’s have witnessed a climb in the incidence of an acute polio-like illness. Preceded by 5 days of a viral prodrome (rhinorrhea, fever, cough), affected children would progress from full strength to flaccid paralysis over the course of hours to days–many of whom would not fully recover. The upper extremities were most commonly involved, and the progression of symptoms do not fit a descending paralysis pattern (such as you might see in infant botulism or myasthenia gravis). Imaging of the spine would confirm these symptoms to be related to an anterior horn transverse myelitis. Dr. Ana Cristancho, who previously reported on the Zika virus, spoke with infectious disease expert, Dr. Sarah Hopkins, in our latest BrainWaves episode:
The clinical and diagnostic course of acute flaccid myelitis (AFM), as it has been called, is summarized in this diagram from Messacar and colleagues.
The transverse myelitis observed in these several hundred cases is unique from the typical cases of
transverse myelitis seen in multiple sclerosis and numerous other inflammatory diseases. Not only does it have a proclivity to affect the anterior horn cells–resulting in flaccid weakness without any sensory involvement–but the lesions are longitudinally extensive, similar to those of neuromyelitis optica. According to multi-center data, 90% of cases had more than 3 vertebral segments involved, and the median number of segments was between 10 and 17. As we’ve shown in the figure to the right, there are several other considerations for pure anterior horn cell disease, and among the infections you should be considering west nile virus, poliomyelitis, tick paralysis, and enterovirus 71 and 68 strains. But even these infectious causes of myelitis rarely produce such longitudinally extensive lesions with such devastating clinical outcomes. Other features of AFM include an asymmetric pattern of the weakness and lack of responsiveness to traditional therapeutics for transverse myelitis (intravenous immune globulin, steroids, and plasmapheresis). That being said, experts recommend the use of IV Ig, with fluoxetine (for reasons that are discussed in the podcast), for cases suspected of AFM.
What is still incompletely understood is the causative agent of AFM. Epidemiologic data support the association between enterovirus 68 and AFM, similar in quality to the association between Zika virus and the guillain-barre syndrome. In its simplest terms, we have found that patients with AFM (or GBS) appear to have been exposed to enterovirus 68 (or Zika) in the preceding days or weeks, but less is known about the patients who have been exposed to these infectious agents and develop no symptoms. Therefore, a causal relationship remains highly controversial and no clear, triggering mechanism has been confirmed for AFM to date.
Until we’ve learned more about AFM, I definitely recommend you check out this episode on the latest that is known about this polio-like illness. And stay tuned, there’s much more to come as we more systematically analyze this outbreak in the US.
Aliabadi N, Messacar K, Pastula DM, Robinson CC, Leshem E, Sejvar JJ, Nix WA, Oberste MS, Feikin DR and Dominguez SR. Enterovirus D68 Infection in Children with Acute Flaccid Myelitis, Colorado, USA, 2014. Emerg Infect Dis. 2016;22:1387-94.
Greninger AL, Naccache SN, Messacar K, Clayton A, Yu G, Somasekar S, Federman S, Stryke D, Anderson C, Yagi S, Messenger S, Wadford D, Xia D, Watt JP, Van Haren K, Dominguez SR, Glaser C, Aldrovandi G and Chiu CY. A novel outbreak enterovirus D68 strain associated with acute flaccid myelitis cases in the USA (2012-14): a retrospective cohort study. Lancet Infect Dis. 2015;15:671-82.
Messacar K, Schreiner TL, Van Haren K, Yang M, Glaser CA, Tyler KL and Dominguez SR. Acute flaccid myelitis: A clinical review of US cases 2012-2015. Annals of neurology. 2016;80:326-38.