A mysterious syndrome that paralyzed kids seems to have disappeared, but why?

A syndrome that paralyzed children in Colorado and across the nation seems to have disappeared almost as mysteriously as it arrived, leaving scientists to figure out what happened and survivors to adapt as they grow up.

Doctors first identified cases of unexplained muscle weakness and limb paralysis in children, which they called acute flaccid myelitis, or AFM, in 2014—though in retrospect, sporadic cases showed up as early as 2009, said Dr. Kevin Messacar, an infectious disease specialist at Children’s Hospital Colorado. The hospital was one of the first to raise alarms that something unusual was going on.

Nationwide, cases spiked again in 2016 and 2018, with only a handful recorded in odd-numbered years, according to data from the Centers for Disease Control and Prevention.

But the pattern broke in 2020, possibly because measures to combat COVID-19 kept kids from getting other viruses, and while the most likely culprit virus returned in 2022, the expected cases of paralysis didn’t.

Last year, the CDC recorded 18 confirmed cases of AFM, down from a high of 238 in 2018. Colorado has ranged from zero to four cases each year since 2018, when the state recorded 17.

The evidence linking the syndrome to infection by the common respiratory bug enterovirus D68 has only grown, raising questions about whether the virus itself changed, kids’ immune systems are responding differently, or some other environmental factor tipped the balance, Messacar said.

Typically, EV-D68 causes colds, but for unknown reasons, it infected the spinal cord and caused muscle weakness and paralysis in a small percentage of kids.

“It may not be as straightforward as one of those three factors,” with multiple changes contributing, he said.

No cure exists for AFM, and children who had it vary in how much they’ve recovered.

Lydia Pilarowski, a 16-year-old who lives in Denver, had one of the earlier known cases in August 2014.

She and her brother both had what seemed like ordinary colds, but Lydia remained lethargic after her brother recovered. Then their mother, pediatrician Dr. Sarah Lacey, started noticing Lydia couldn’t do things she did before, like turning while riding her bike or playing the piano with her left hand.

“That’s suddenly when it dawned on me that something was wrong,” Lacey said.

Certain muscles in her upper arm no longer obeyed her brain’s commands to move, so Lydia has worked with occupational therapists over the years to strengthen the other muscles and find creative ways to do the things she wants to.

For example, when she was skiing competitively, Lydia noticed her left arm was dragging in the wind and slowing her down. She initially wasn’t sure how people would react to her skiing with her arm in a sling—a clear marker of an otherwise invisible disability—but it improved her times and was freeing in its own way, she said.

“Instead of trying to work through something I can never work through, I work around it and work with it to do the things I love,” Lydia said.

The process of learning how to live with the after-effects of AFM never really ends, Lacey said.

As Lydia tries more things, they confront new challenges, such as how to put a suitcase in a plane’s overhead bin when one arm won’t go over her head. They also recently learned that the syndrome had subtle effects on Lydia’s diaphragm, contributing to shortness of breath that Lacey initially thought more cardiovascular training would resolve.

“There are so many things we don’t know,” Lydia said.

While AFM seems to have gone away as an immediate public health concern for the moment, researchers are still trying to understand it, said Dr. Carlos Pardo, a professor of neurology and pathology at John Hopkins University’s School of Medicine.

Right now, one of the top theories is that a different variant of EV-D68 emerged in the early 2010s, causing paralysis in rare cases, he said.

A research lab on the University of Colorado’s Anschutz Medical Campus is working on comparing samples of EV-D68 that cause paralysis in at least some cases and others that don’t, Messacar said.

They’ve found only a small number of mutations between the two variants, and are studying whether any of those could have made the critical difference. If they do prove important, that information could help detect if more-dangerous variants return or even lead to new vaccines, he said.

Another possibility is that EV-D68 could always cause paralysis in rare cases. Other syndromes cause the same symptoms, so it could be that doctors simply didn’t pick up that a virus might be the root cause, Pardo said.

The syndrome’s seeming disappearance also could have at least two possible explanations, Pardo said. Maybe it couldn’t hang on during the early years of the pandemic, when people weren’t spreading it, and different variants replaced it. Or, maybe enough people now have immunity from a large wave of EV-D68 that the number who are susceptible to that variant dropped dramatically, he said.

While scientists still don’t know everything they would like to about AFM, they’ve made significant progress since 2014, when they didn’t even have a test that could detect whether the virus had gotten into someone’s spinal fluid, Messacar said. An antibody-based treatment for EV-D68 is going through trials, and more than one possible vaccine is approaching human testing, he said.

Lydia said she hopes researchers can learn more about what caused the wave of AFM cases, both for her own understanding and to prevent something similar from happening again. But that the uncertainty is something she’s had to “make peace” with, using the same skills that help her adapt to each new challenge that arises from her disability.

“I think growing up, you have these preconceived notions about what your life will look like,” she said. “For me, it’s been about embracing the unknown.”

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