Acute Flaccid Myelitis Surged in 2018: What CDC Found in 80 Confirmed Cases

Acute flaccid myelitis (AFM) is a rare condition: rapid onset of flaccid weakness in one or more limbs, with lesions in the spinal cord's gray matter. CDC has tracked it with a standard case definition since 2014. In August 2018, reports of possible AFM were running higher than in August 2017, and on August 23 CDC alerted clinicians through Epi-X, asking them to watch for and report cases.

How cases are classified

Anyone with acute flaccid limb weakness meets the clinical criteria, and is then classed by the Council of State and Territorial Epidemiologists' definitions as:

• confirmed — an MRI showing a spinal cord lesion mostly in gray matter, spanning at least one spinal segment;
• probable — pleocytosis in the cerebrospinal fluid (CSF), more than 5 white blood cells per mm³;
• or not a case.

The 2018 cases

From January 1 to November 2, 2018, 106 patients were classified: 80 confirmed (from 25 states), 6 probable and 20 not cases — three times as many confirmed cases as in the same period of 2017.

Confirmed AFM cases by month of onset, 2018 (counts as of November 2, 2018, and subject to change). Image from the Centers for Disease Control and Prevention

Who: median age 4 years (range 7 months to 32 years); 47 (59%) male; of 65 with race recorded, 56 (86%) white.

Before the weakness — in the preceding four weeks, 79 (99%) had signs of a viral illness:

Which limbs:

Severity: all 80 were hospitalized; 47 (59%) needed intensive care. No deaths were reported.

Spinal fluid: of 78 with CSF results, 65 (83%) had pleocytosis (median 103 cells per mm³), mostly lymphocytes. Median CSF protein was 47 mg/dL (normal under 45) and glucose 59 mg/dL (normal 40 or more). CSF was usually collected about 1 day after weakness began.

The search for a virus

CDC tests for enteroviruses and rhinoviruses (EV/RV) in every patient meeting the clinical criteria, when specimens are available. For 71 of the 80 confirmed cases, 125 specimens were tested — 21 CSF, 59 respiratory and 45 stool or rectal swabs.

• 38 patients (54%) tested positive: EV-A71 in 11, EV-D68 in 14, and other viruses in 13 — mostly from nonsterile sites.
• Only two CSF specimens were positive — one for EV-A71, one for EV-D68. A virus found in CSF would be considered the cause; such findings are rare.
• All stool specimens were negative for poliovirus.

Why suspect viruses? Some enteroviruses can cause sudden limb weakness, and AFM rose alongside a nationwide EV-D68 respiratory outbreak in 2014. But AFM peaked again in 2016 without reports of big respiratory outbreaks. Nearly every patient had a viral-type illness first, and the evidence so far points to a viral association — CDC and partners are still investigating causes and risk factors.

What to do

• Parents and caregivers: get immediate medical care for a child who suddenly develops weakness in the arms or legs.
• Clinicians: ask about recent fever, with or without respiratory or gut symptoms, and collect CSF, serum, respiratory and stool specimens promptly for viral testing.
• Report every patient with acute flaccid limb weakness to the health department as soon as possible, whatever the lab or MRI results.

Sources

Based on "Increase in Acute Flaccid Myelitis — United States, 2018," by Susannah L. McKay, Adria D. Lee, Adriana S. Lopez and colleagues, Morbidity and Mortality Weekly Report 67(45), Centers for Disease Control and Prevention; a work of the United States government in the public domain. The text and table describe the mixed-virus respiratory specimens differently, so those details are left out.