In the past month, six children in Minnesota have been diagnosed with a rare, potentially paralyzing and deadly nervous system condition called acute flaccid myelitis (AFM), prompting an investigation by the Minnesota Department of Health (MDH).

Currently, little is known about how AMF develops and there are no specific treatments. Though medical researchers believe environmental toxins and genetics may come into play as well, the condition appears to arise as a complication of certain viral respiratory infections in children – very few adult cases have been reported. Viruses in the enterovirus genus – a group that includes the common cold and the polio virus – are most closely associated with AFM, though past cases have also been linked to West Nile virus, Japanese encephalitis virus, Saint Louis encephalitis, and adenoviruses.  

According to a statement released by the agency, the state normally sees about one case of AFM per year, though there was a nationwide spike in 2014 following an outbreak of an enterovirus called EV-68. CNN reports that there were 120 total cases nationwide in 2014, but only 21 in 2015.

The onset of AFM is characterized by sudden weakness or paralysis in one or more limbs, sometimes accompanied by neck weakness or stiffness, drooping eyelids or other facial muscles, difficulty swallowing, and/or slurred speech. Per the Centers for Disease Control and Prevention (CDC), the most severe symptom of AFM is respiratory failure caused by weakening of the diaphragm muscles. If this begins to occur, the patient requires urgent medical intervention so they can be placed on a ventilator. In a small number of cases, the processes driving AFM have triggered other serious neurologic complications, leading to death.

These impairments are caused by lesions in the gray matter of the brain and spinal cord, a diagnostic sign that may be detected on MRI scans. Most affected individuals also show increased immune cells in their cerebrospinal fluid. No past patients have shown changes in cognition or mental state.

“What we’re looking at is a disease indistinguishable in most respects from traditional polio, in terms of its symptoms,” Dr Keith Van Haren, a pediatric neurologist at Stanford University School of Medicine, told Neurology Today in 2014. “Until now it was a really rare bird. Before 2012, we saw maybe one case every five years that wasn’t attributable to West Nile. Since 2012, we’ve seen many more cases. And since just this summer, we’ve seen even more.”

The long-term prognosis for AFM patients is not known at this time. Treatment varies on a case-by-case basis and typically centers on physical therapy to regain strength in the affected limb(s) and other muscles.

The Minnesota Department of Health are now looking into common factors between the six children in Minnesota, all of whom are under 10 years old. They ask parents to keep an eye out for potential AFM symptoms in their children and to bring them in for an urgent exam if any appear.