From the Journals

Viral cause of acute flaccid myelitis eludes detection



A study of 305 cases of acute flaccid myelitis has found further evidence of a viral etiology but is yet to identify a single pathogen as the primary cause.

Writing in Pediatrics, researchers published an analysis of patients presenting with acute flaccid limb weakness from January 2015 to December 2017 across 43 states.

A total of 25 cases were judged as probable for acute flaccid myelitis (AFM) because they met clinical criteria and had a white blood cell count above 5 cells per mm3 in cerebrospinal fluid, while 193 were judged as confirmed cases based on the additional presence of spinal cord gray matter lesions on MRI.

Overall, 83% of patients had experienced fever, cough, runny nose, vomiting, and/or diarrhea for a median of 5 days before limb weakness began. Two-thirds of patients had experienced a respiratory illness, 62% had experienced a fever, and 29% had experienced gastrointestinal illness.

Overall, 47% of the 193 patients who had specimens tested at a Centers for Disease Control and Prevention or non-CDC laboratory had a pathogen found at any site, 10% had a pathogen detected from a sterile site such as cerebrospinal fluid or sera, and 42% had a pathogen detected from a nonsterile site.

Among 72 patients who had serum specimens tested at the CDC, 2 were positive for enteroviruses. Among the 90 patients who had upper respiratory specimens tested, 36% were positive for either enteroviruses or rhinoviruses.

A number of stool specimens were also tested; 15% were positive for enteroviruses or rhinoviruses and one was positive for parechovirus.

Cerebrospinal fluid was tested in 170 patients, of which 4 were positive for enteroviruses. The testing also found adenovirus, Epstein-Barr virus, human herpesvirus 6, and mycoplasma in six patients. Sera testing of 123 patients found 9 were positive for enteroviruses, West Nile virus, mycoplasma, and coxsackievirus B.

“In our summary of national AFM surveillance from 2015 to 2017, we demonstrate that cases were widely distributed across the United States, the majority of cases occurred in late summer or fall, children were predominantly affected, there is a spectrum of clinical severity, and no single pathogen was identified as the primary cause of AFM,” wrote Tracy Ayers, PhD, from the National Center for Immunization and Respiratory Diseases, and coauthors. “We conclude that symptoms of a viral syndrome within the week before limb weakness, detection of viral pathogens from sterile and nonsterile sites from almost half of patients, and seasonality of AFM incidence, particularly during the 2016 peak year, strongly suggest a viral etiology, including [enteroviruses].”

The authors of an accompanying editorial noted that the clinical syndrome of acute flaccid paralysis caused by myelitis in the gray matter of the spinal cord has previously been associated with a range of viruses, including poliovirus, enteroviruses, and flaviviruses, so a single etiology to explain all cases would not be expected.

“The central question remains: What is driving seasonal biennial nationwide outbreaks of AFM since 2014?” wrote Kevin Messaca, MD, and colleagues from the University of Colorado at Denver, Aurora.

Two authors declared consultancies, grants, and research contracts with the pharmaceutical sector. No other conflicts of interest were declared. One editorial author declared funding from the National Institute of Allergy and Infectious Diseases.

SOURCE: Ayers T et al. Pediatrics. 2019 Oct 7. doi: 10.1542/peds.2019-1619.

*Updated 10/14/2019.

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