Staying alert to the rare but real risks of acute flaccid myelitis

Sarah Hopkins, a pediatric neurologist at the Perelman School of Medicine and Children’s Hospital of Philadelphia, has seen an increase in cases of the paralyzing condition this year. She explains what parents and pediatricians should watch for.

Visit any preschool or day-care center this time of year and you’ll encounter coughs and runny noses. The overwhelming majority of these children will bounce right back from their infection. But during the last few months, several dozen children—and a few adults—around the nation have developed acute flaccid myelitis (AFM), a polio-like disease, following mild respiratory illnesses. As of the end of last week, the U.S. Centers for Disease Control and Prevention (CDC) has confirmed 80 AFM cases so far in 2018.

AFM is characterized by lasting and often progressive weakness in an arm or leg, and the CDC has yet to make a firm call about what is causing the rare but serious condition. Many researchers, however, suspect a tie to a common virus. Sarah Hopkins, a pediatric neurologist at the Children’s Hospital of Philadelphia (CHOP) and the Perelman School of Medicine, has seen several children with AFM so far this year. In a conversation with Penn Today, she explains what we know about the disease, how doctors and scientists are responding, and what symptoms should raise alarm.

Sarah Hopkins
Sarah Hopkins


Can you describe what characterizes this condition?

Acute flaccid myelitis is defined as an acute onset of paralysis in a setting of an abnormal spinal cord MRI, with a lesion that affects the central gray matter of the spinal cord. That’s important because the central gray matter is where the motor neurons begin and radiate out into the limbs.

Basically, these kids have an illness that’s very similar to polio, with sudden weakness in their arms or legs.

And what do we know about what causes it? Why is this still labeled mysterious?

We’ve known about acute flaccid myelitis since 2014, maybe even as early as 2012 when there were some suspected cases in California. Cases seem to spike every other year. And always in the fall. We see it from August through November, with most cases by the end of October, so we’re hopefully through the worst of it now.

These spikes occur in years that have more enteroviruses circulating, so that’s how the connection started to be made that enterovirus might be responsible. But it’s complicated. On one hand, we saw a spike in AFM in 2016, for example, but didn’t see high levels of enterovirus circulating nationally. On the other hand, researchers at the University of Colorado developed a mouse model of AFM and found if you gave them the particular enterovirus that had been circulating among children in a year with high rates of AFM, some of them developed the condition.

For most people, infection with an enterovirus is just a common cold. Enterovirus 71, which also seems to be implicated in some cases of AFM, causes hand, foot and mouth disease. But we suspect there is something about certain people that make them prone to paralysis. Either their immune system takes a bit longer to respond to the virus, or there’s just something different about their immunochemistry that doesn’t respond as well. We’re working to understand that.

What has this year looked like at CHOP in terms of AFM?

We’re a big tertiary center so we see patients from all over. This isn’t necessarily an outbreak where we’re seeing a bunch of kids with this all from one town; it’s kids from all over the tri-state region.

At CHOP, we look for enterovirus pretty aggressively in our patients’ nasopharyngeal secretions [mucus], and in 2016 we found enterovirus in every child presenting with AFM. To me that seems pretty compelling that there is a connection; it’s hard to ascribe that to chance. 

The CDC is reluctant to make the connection because we’re not seeing the virus in the cerebral spinal fluid, but then again polio was hard to find in spinal fluid, too. My inclination is that there’s at least a connection. But there are other viruses that can cause this clinical picture; West Nile Virus is one.

What age are you seeing this in most commonly?

Typically it’s younger kids, 3- and 4-year olds. Sometimes we see it in little babies. We’ve seen a scattering of older kids, teenagers, and there have been a couple of adult cases confirmed by the CDC.

This is a pretty scary thing to read about, especially for parents who may worry if their child has cold symptoms. How concerned should we be?

I think it’s really important to get the word out so that parents and primary-care physicians are alert if they see a kid with a viral illness and a little bit of weakness. Sometimes even if the child ends up seeing a doctor, if the child doesn’t get a workup for spinal cord lesions, the doctor may not catch it.

We don’t want parents to be concerned every time the child has a cold because the vast majority of kids are totally fine. But if you notice a child is not moving one arm very well, or is using one arm to move the other, or they have a new limp or are refusing to walk, or have facial weakness or their speech isn’t normal, then you should be concerned and bring them into a hospital as soon as possible.

How quickly?

Sometimes a matter of hours can make a difference. The main urgency to bring them in is they can have respiratory decompensation. If they start having trouble breathing you want them to be in a hospital setting where that can be managed.

What else can be done for these patients? Are there any effective treatments?

There have been no clinical trials that have looked at this yet because it’s still so new. Treatments that work for a similar condition, transverse myelitis, don’t seem to work as well for acute flaccid myelitis.

One thing we do is provide intravenous immunoglobulin (IVIG), which is essentially pooled antibodies from blood donors. The idea is that we might be able to boost the immune system and hope to shorten the course of the infection and keep the spinal cord involvement from progressing. 

In a mouse model, animals that got the antibodies quickly did better. Right now our target is to shorten the window between a patient being admitted and receiving that treatment. Our latest patients came in and within three or four hours of being here had IVIG. That’s impressive.

What kind of work is being done to develop better treatments?

 I’m involved in an acute flaccid myelitis working group, with doctors from multiple institutions nationwide. It’s hard because there are cases scattered all around the country. This year we saw a bunch in Wisconsin; they hadn’t really had any cases before. But because we had so many cases here at CHOP in 2016, we are set up and have thought about what we’re going to do. The goal is to learn from each other.

There’s a lot of push for more research. What we do here is collect standardized information—with consent, of course—from patients on their clinical presentation and outcome over the following year. We also collect blood samples for our biorepository. Some are kept at CHOP and others are sent to Penn, and stored for future use. There’s been more of a trend to do that at other institutions as well. 

There’s also a study of genetics going on at Johns Hopkins that we refer patients to that’s working on finding out what individual differences might predispose people to getting AFM. Other centers, including the University of California, San Francisco, are looking deeper into specific viral association. 

Any last takeaways for readers?

The main thing to know is that tons of people have this virus or have had this virus and are totally fine. It’s really only one in a million or one in hundreds of thousands of cases that we see this. But if your child is developing any weakness—whether or not they have respiratory symptoms—we’d rather see them sooner than later. If it were my child and I saw that, I’d take them to the emergency room.


Sarah Hopkins is a pediatric neurologist and section head for multiple sclerosis and neuroinflammatory disorders at the Children’s Hospital of Philadelphia and is an assistant professor of clinical neurology at Penn’s Perelman School of Medicine.