Mysterious polio-like paralysis increasing in California and elsewhere

By John Murphy, MDLinx
Published December 22, 2015

Key Takeaways

Reported cases of acute flaccid myelitis, which has no known cause, have significantly increased in California and in other states in the past year, according to a study published December 22, 2015 in JAMA.

Acute flaccid myelitis is characterized as acute onset of flaccid weakness in 1 or more limbs and evidence of a spinal gray matter lesion on MRI, and mostly affects children or teens. While it appears similar to polio, its cause is unknown.

In fall of 2012, the California Department of Public Health (CDPH) received 3 separate reports of acute flaccid paralysis cases with evidence of spinal motor neuron injury. Consequently, the CDPH increased its surveillance for similar cases hoping to study and identify possible causes of this syndrome.

In August 2014, the Centers for Disease Control and Prevention (CDC) began nationwide surveillance of acute flaccid myelitis cases. As of July 2015 (the most recent data available), the CDC had verified reports of 120 cases in 34 states.

In this study, Keith Van Haren, MD, Assistant Professor of Neurology at Stanford University Medical Center, Palo Alto, CA, and colleagues summarized cases of acute flaccid myelitis/paralysis in patients with findings of spinal motor neuron involvement reported from June 2012 to July 2015 in California. In all cases, cerebrospinal fluid, serum samples, nasopharyngeal swab specimens, and stool specimens were submitted to the state laboratory for infectious agent testing.

The researchers identified 59 cases in California during the 3-year period. In 50 of the cases, patients were younger than 21 (median age was 9 years). Two patients, both immunocompromised adults, died within 60 days of symptom onset. Symptoms that occurred before (or during) onset of neurological symptoms included respiratory or gastrointestinal illness (54 patients), fever (47 patients), and muscle pain (41 patients). Among 45 patients with follow-up data, 38 had persistent weakness at a median follow-up of 9 months.

“Although the syndrome described is largely indistinguishable from poliomyelitis on clinical grounds, epidemiological and laboratory studies have effectively excluded poliovirus as an etiology,” the researchers noted.

The most frequently detected pathogen in nasopharynx swab specimens, stool specimens, or serum samples was enterovirus (15 of 45 patients tested). Of these, 9 patients tested positive for enterovirus D68. Also, the incidence of acute flaccid myelitis cases was significantly higher during a national enterovirus D68 outbreak (August 2014-January 2015) compared with other monitoring periods.

Still, the etiology of acute flaccid myelitis cases remains undetermined, the researchers wrote.

Whether there are any similarities among patients who recovered, and whether such an association holds a clue to the mysterious syndrome’s etiology, is “the million dollar question,” Dr. Van Haren said.

“Unfortunately, our data weren’t really designed to answer this question,” he added. “Nonetheless, it is worth noting that the degree of weakness ranged from total paralysis to mild weakness. At least one of the cases who made a full recovery had a milder degree of weakness at the outset.”

The researchers note that “ongoing surveillance efforts are required to understand the full and potentially evolving levels of infectious agent-associated morbidity and mortality.”

“To our knowledge,” the authors wrote, “the California surveillance program for acute flaccid paralysis is the first to use specific case criteria and report subsequent incidence data for the subset of paralysis cases attributable solely to acute flaccid myelitis and may serve as a guide for similar surveillance efforts in the future.”

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