Why have some American kids been paralyzed for a year? Doctors are trying to find out.

Imagine you have a pre-adolescent son or daughter who comes down with what seems like a nasty case of the flu. Then, without warning, a new, more troublesome symptom develops: Your 8-year-old daughter collapses, unable to move her leg; your 6-year-old son suddenly stops moving his right arm. It lays limp by his side.

It’s a nightmare scenario for any parent — and a sad reality for some.

Those two scenarios actually happened to children who contracted the EV-D68 virus in the United States last fall. The enterovirus spread through the country in the second half of 2014. For most children, it seemed merely like a bad case of the flu. But for a group of about 100 kids, it came with a severe symptom: a polio-like paralysis in the arms and legs.

EV-D68 isn't a new virus, but paralysis had never been reported with the virus before. Doctors are still baffled by what caused it, and the children who experienced it have yet to fully recover.

The mystery only deepened after doctors conducted MRI tests on the afflicted children. The tests detected what Teri Schreiner, an assistant professor of neurology at the University of Colorado in Denver, called a “signal change” — a type of inflammation in the front part of the spinal cord that is involved in controlling movement. This was not what doctors would expect to see when there is inflammation of the spinal cord, Schreiner said.

There was one compelling clue: The EV-D68 virus is in the same family as the polio virus, so it seemed reasonable that it was behind the paralysis, which doctors labeled “acute flaccid myelitis.” But since not all children who got the virus had the paralysis, Schreiner and her colleagues couldn’t make a definitive connection.

“What we know is that there were two outbreaks occurring at the same time: The outbreak of enterovirus D68 causing the respiratory illness, and the outbreak of the syndrome that we're calling acute flaccid myelitis,” Schreiner says. “And what we're trying to do now is establish that one caused the other, and we're doing that through several means.”

Doctors are pursuing three avenues to tackle this question. One is a large case study comparing the paralyzed children with kids who had the virus but did not have the paralysis. The doctors hope to determine what factors or differences could have led the one group to develop paralysis while the other did not.

They're also studying the makeup of the virus to determine how it might be similar or different from other viruses in its family, including polio. Finally, they're looking at families in which two siblings came down with the virus but only one of the children developed paralysis.

In the meantime, the children affected by paralysis have generally made some improvements, but the phenomenon is so new that doctors can’t give the families a solid sense of what is going to happen next. It’s a frustrating situation for the parents and the doctors, but they’re trying to remain optimistic.

“We don't have enough information about prior cases of acute flaccid myelitis to really project and say, in one year your child is going to look like this, in two years your child will look like that, and so forth,” says Schreiner. “So one of the things that we're focusing on is, first of all, providing as much support to the families and the patients as possible in terms of psycho-social and emotional health — but also physical therapy, occupational therapy, and really following the children closely to see if we can maximize their recovery and help them to recover from this illness.”

This story is based on an interview from PRI's Science Friday with Ira Flatow