Across the country, a mysterious illness that looks a lot like polio is causing varying degrees of paralysis, mostly in children. This is just about the only definitive statement there is to make at this point about the syndrome, dubbed acute flaccid myelitis, because the rest of the details are rife with contradictions.
Sometimes, the children mostly recover from the paralysis; sometimes, they don’t. Sometimes, the symptoms appear after the child is getting over enterovirus D-68, the respiratory illness that circulated throughout the country this summer and fall; sometimes, the patients never had EV-D68. Some experts believe the cases are tapering off and aren’t likely to reappear next summer; others think a bigger outbreak could be just around the corner. And while almost all of the cases so far have been in children, a handful of adults have been diagnosed with the syndrome, too.
At the latest count, there have been 57 cases, according to Dr. Max Witnitzer, a pediatric neurologist who co-presented a session on acute flaccid myelitis at last week’s meeting of the Child Neurology Society. During that presentation, Witnitzer asked for anyone who’d seen the illness in their own practice to raise their hand, as a way to do an informal poll. He estimates that more than 70 hands raised, which may suggest that there are more cases than have been reported.
Although it’s not clear what’s triggering the illness, neurologists are easily able to spot it in an MRI and make a diagnosis. “The part of the nervous system that’s affected by the infection is the anterior horn cell, in the spinal cord,” Witnitzer said. “Now, the anterior horn cell’s job is to regulate muscle function.” So if these cells are damaged, muscle weakness — paralysis — occurs. In some cases, the muscle weakness is moderate or mild, affecting one or two limbs. In others, it’s been severe enough to require a ventilator.
The illness is called acute flaccid myelitis because it shows up suddenly (acute) and results in muscle weakness (flaccid) because of an inflammation to the spinal cord (myelitis). And neurologists realize this is an unwieldy name. “The alternate term is polio-like illness, but we’re trying not to use that too much,” said Dr. Keith Van Haren, a Stanford University neurologist. For those in medicine, the term is imprecise, and, therefore, confusing. For those not in medicine, the association with the polio epidemics of the 1930s, ‘40s and early ‘50s is alarming. “But that is what we’re really describing here — that weakness that was associated with polio.”
The virus that causes polio is in the same family of viruses as EV-D68, which was seen in a nationwide outbreak this year, infecting more than 1,100 people in 47 states and the District of Columbia. So far, EV-D68 is experts’ best guess at what’s behind these cases of paralysis. But the virus isn’t showing up in blood or spinal fluid tests, so it could be something else entirely. If it is caused by an enterovirus, there will likely be fewer new cases of acute flaccid myelitis in the coming weeks and months, because enteroviruses tend to circulate in the summer and early fall.
To be clear, this illness is still very rare, and it isn’t new — a handful of cases pop up every year. But there are more cases this year than have ever been seen before, which is why neurologists are concerned. The U.S. Centers for Disease Control continues to investigate, but for now, it’s mostly a mystery.