Mystery Still Swirling Around Acute Flaccid Myelitis

By Christopher Cheney

Acute flaccid myelitis is a polio-like illness that has afflicted about 400 children over the past four years. There is no known cause. There is no known cure.

“There are currently no targeted therapies or interventions with enough evidence to endorse or discourage their use. We recommend that clinicians expedite neurology and infectious disease consultations to discuss treatment and management,” Nancy Messonnier, MD, director of the National Center for Immunization and Respiratory Diseases, said in a briefing last week.

The rare neurological disorder—less than 1 in a million Americans contract AFM annually—mimics polio with weakness in one or more limbs. Some patients have recovered quickly. Paralysis has persisted in others.

Most of the confirmed AFM cases have been in children, according to the Centers for Disease Control and Prevention (CDC). As of November 5, there were 80 confirmed cases this year, mostly in children between 2 and 8 years old, Messonnier said.

“As a mom, I know what it is like to be scared for your child, and I understand parents want answers. CDC is a science-driven agency. Right now, the science doesn’t give us an answer,” she said.

Limited treatment options

The CDC plans to release new treatment and care management guidance this week, Messonnier said.

“Since 2014, we have been working with clinicians treating AFM patients. In the next day or two, we are posting updated considerations that reflect the significant experience of those clinicians. Unfortunately, because we don’t yet know the cause of all AFM cases, these considerations are not as specific as we would like,” she said.

The CDC issued interim considerations for clinical management of AFM in November 2014. Although clinicians had tried corticosteroids, plasmapheresis, interferon, antivirals, and other targeted therapies, none of them were deemed safe or effective in the treatment of AFM.

The interim considerations include three primary recommendations for clinical management:

  • Patients with respiratory muscle weakness should be considered for ICU admission
  • Patients undergoing MRI should be closely checked with methods including telemetry, pulse oximetry, and blood pressure monitoring
  • As soon as patients are clinically stable, they should undergo intensive physical therapy, which could improve functional outcomes and prevent muscular atrophy, joint contractures, and other conditions resulting from severe and persistent limb weakness

Search for a cause

Diagnosis of AFM is primarily clinical—patients present the sudden onset of flaccid limb weakness—and MRI exam results showing spinal cord lesions mainly in gray matter and spanning at least one vertebral segment.

The CDC cautions that an initial MRI of an AFM patient may not show spinal cord lesions, which may not appear until 72 hours after the onset of flaccid limbs.

Viral infection has been a suspected cause of AFM since the first outbreaks of the illness in 2014.

Viruses are the suspected cause of at least two AFM cases this year, Messonnier said. In these cases, spinal cord fluid tested positive for two viruses.

“One had evidence of EVA-71 and one had evidence of EVD-68. One of the cases was an adult who was on immuno-depressive medication, and the other was in a child who had very rapid progression of paralysis,” she said.

The findings are clues rather than definitive signs of a cause for AFM, Messonnier said.

“When a pathogen is found in the spinal fluid, it is good evidence that it was the cause of the patient’s illness. However, oftentimes despite extensive testing no pathogens are found in the spinal fluid. This may be because the pathogen has been cleared by the body or it is in hiding in tissues that make it difficult to detect. Another possibility is that the pathogen triggers an immune response in the body that causes damage to the spinal cord.”