11/15/2018 12:22 EST | Updated 11/15/2018 12:22 EST

Cases Of Acute Flaccid Myelitis, A Polio-Like Illness Causing Paralysis In Kids, Continue To Rise

U.S. officials are probing whether a virus or auto-immune disorder may be to blame.

Puzzled by a rise in U.S. children with sudden paralysis in their arms or legs, health officials are probing whether a virus or auto-immune disorder may be to blame.

A total of 252 cases of the disorder known as acute flaccid myelitis (AFM) are currently under investigation in the U.S., an increase of 33 since last week, said Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the U.S. Centers for Disease Control and Prevention (CDC), in a Tuesday news conference.

With 80 confirmed cases so far this year, 2018 looks to be on pace with prior peak years like 2014 (120 cases) and 2016 (149 cases), Messonnier said. More than 400 cases have been confirmed through lab tests since 2014, the first year the syndrome emerged. A couple dozen cases were confirmed in 2015 and 2017.

Messonnier said she understands parents' alarm but stressed that the disorder remains "rare."

Keith Brofsky/Getty Images
Acue flaccid myelitis causes paralysis in children.

Most cases involve children aged two to eight. Almost all complained of fever and respiratory illness three to 10 days before suddenly experiencing paralysis in their arms or legs.

For some, the paralysis went away, but at least half have not recovered, said Messonnier.

Cases have been reported in Canada, too

Canadian doctors have also reported a spike in AFM, with several children's hospitals in Ontario and Quebec noting an increase in cases since the summer.

As of Nov. 13, 25 cases of acute flaccid paralysis (AFP) — which can include AFM — have been confirmed in Canada this year, and 23 cases are being investigated, according to new data from the Public Health Agency of Canada. But the agency also notes that on average, there are between 27-51 cases of AFP reported annually in Canada.

In a news release, the Canadian Paediatric Society (CPS) stressed that AFM is still quite rare.

"CPS wishes to assure parents and caregivers that — while a very serious condition — AFM is exceptionally rare. The likelihood of a child being diagnosed is approximately 1:1,000,000," CPS said.

U.S. officials still stumped for a cause of AFM

The CDC has tested 125 spinal cord fluid samples, and half were positive for rhinovirus or enterovirus, which commonly cause symptoms like fever, runny nose, vomiting, diarrhea and body aches. Yet scientists are still stumped about the precise cause of the sudden paralysis, since these viruses are common but AFM is not.

"We are trying to figure out what the triggers are that would cause someone to develop AFM," Messonnier told reporters.

"It may be one of the viruses we have already detected. It may be a virus that we haven't yet detected. Or it could be that the virus is kicking off another process that is actually triggering — through an auto immune process — AFM," she said.

"CDC is a science-driven agency. Right now, the science doesn't give us an answer."

There's no way to prevent AFM

Perhaps most frustrating for parents, there is no way to prevent it, and no targeted therapies or interventions.

"Parents and caregivers are urged to seek immediate medical care for a child who develops sudden weakness of the arms or legs," said the CDC's latest report on AFM, released Tuesday.

Messonnier said the CDC has not been tracking every case of AFM since 2014, leading to gaps in the federal agency's knowledge of the illness, which experts are now trying to fill. One child with AFM is reported to have died in 2017.

With files from Natalie Stechyson

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