Published November 6, 2018
The so-called mystery paralysis that has now affected more than 70 children in the United States this year is understandably causing concern among parents, but it is extremely rare, according to Mark D. Hicar, MD, PhD, assistant professor of pediatrics in the Division of Infectious Diseases.
“Acute flaccid myelitis — or AFM — is very rare,” says Hicar, a pediatric infectious disease physician with Oishei Children’s Hospital and UBMD Pediatrics.
He notes that in 2016 — one of the recent peak years — there were 149 cases of AFM in the U.S. compared to an estimated 128,000 children injured in automobile accidents and 723 automobile deaths in children under 12.
Hicar has treated one probable case of AFM this year and treated one case in 2014.
“AFM is not subtle. It is typically characterized by the sudden onset of ‘flaccid paralysis,’ which appears as a floppy leg or arm with little, if any, muscle tone,” Hicar says. “It can also present with breathing difficulties or loss of muscle tone in the face.”
“AFM generally occurs after a preceding mild illness has dissipated, such as a cold or fever, so the AFM condition itself is not directly infectious,” Hicar adds. “Being in contact with a child who has AFM does not necessarily put you at risk.”
He added that if the patient still has a viral illness, that would be infectious, “but your immune system will likely take care of it without consequence.”
According to Hicar, viruses associated with AFM include adenovirus, West Nile virus, Powassan virus, rabies and enteroviruses, such as polio. Since 1979, no cases of polio have originated in the U.S.
“Currently, we don’t know the cause of the recent clusters in 2014, 2016 and this year, so estimating is difficult, but likely hundreds to thousands of people in the area have already had the same exposure as our case and their immune systems eliminated the threat without issue,” Hicar says.
He notes that preventing viruses — such as West Nile — by using mosquito and tick repellent, hand-washing, staying home when sick and other good hygiene practices typically recommended for avoiding the flu should be followed.
“There likely is something different about children who develop AFM, some mix of the virus they caught, their genetics and maybe another co-infection that allows it to invade their spinal cord, whereas with most people, this will never happen,” he says.
In addition to a physical exam, criteria for diagnosing a confirmed case depends on an MRI showing inflammation of the white matter of the spinal cord and an elevation of white blood cells in the spinal fluid.
Currently, Hicar says, cases are considered possible or probable until they are confirmed by the national AFM surveillance team at the Centers for Disease Control and Prevention.
He says that more than half of those who do develop AFM will have a full or nearly full recovery, while a quarter will experience moderate deficiency and another quarter may not recover.
“The potential for lifelong paralysis of a limb is scary,” Hicar says. “However we need to remember that these are rare events.”