Acute Flaccid Myelitis

Acute Flaccid Myelitis

Having just receive both my 2nd COVID Booster and Flu Vaccinations I have been feeling pretty “immune-ready-for-the-world!” Then, one of my colleagues at Carolinas Medical Center / Levine Children’s Hospital reminded me that there are many more viruses out there… and that they can also do a lot of harm (thank you Michelle Kerr, MPAS, PA-C, DFAAPA). We have previously discussed how the phrase “It’s Just a Virus” needs to be removed from our lexicon, because it neither conveys empathy nor reassurance. We have many examples of substantial issues related to viral illness (ex, Guillain-Barre, Myocarditis, Mollaret Meningitis, Severe Hand-Foot-Mouth Disease, Myositis), but in the past few years another condition has started to garner attention. Let us digest a quick tasty morsel on Acute Flaccid Myelitis:

Acute Flaccid Myelitis: Basics

Definition of:
  • In 2014, the term “Acute Flaccid Myelitis” was coined and aimed to help characterize presentations that were similar to Polio, but without poliovirus being found. [Ayers, 2019]
    • Until the 1950’s, Polio was a leading cause of Acute Flaccid Paralysis in the US.
      • Then… came… VACCINES in 1955!
    • In summer of 2014, there were several cases of Acute Flaccid Paralysis in Colorado. [Ayers, 2019]
      • Extensive testing did not reveal clear etiology, but…
      • Concurrent outbreak of Enterovirus EV-D68 was noted to be associated.
    • Subsequent outbreak occurrences peak in Late summer to Early Fall.
  • The Center for Disease Control defines Acute Flaccid Myelitis (AFM) as: [Vawter-Lee, 2021]
    • Acute Flaccid Limb Weakness with
    • Spinal Cord Lesions in the Gray Matter on MRI
    • There may be some white matter involvement.
    • Alternative diagnoses ruled-out.
Presentation of:
  • It starts like so many other stories… with a Viral Prodrome!
    • Upper respiratory and/or Gastrointestinal symptoms are common.
    • Symptoms often precede development of AFM by 1 to 2 weeks.
  • Weakness develops rapidly.
    • May be one or more extremities
    • Often more proximal weakness (so don’t just check for grip strength!)
    • Loss of muscle tone and deep tendon reflexes can be seen (so… check DTRs!)
  • Other findings can also occur:
    • Pain in the affected extremity
    • Headache
    • Stiff neck
    • Cranial Nerves can be involved
      • Facial droop
      • Difficulty moving eyes
      • Difficulty swallowing
      • Slurred speech
      • Weak cry
Complications of:
  • Respiratory distress (can progress rapidly… so these children do not get discharged!)
  • Hemodynamic and Temperature instability and other Neurologic decompensation
Associated with:
  • Non-polio enteroviruses (EV-D68, EV-A71), Coxsackieviruses
  • Flaviviruses (West Nile virus, Japanese encephalitis virus)
  • Herpesviruses
  • Adenoviruses

Acute Flaccid Myelitis: Distinct from GBS?

  • Distinguishing between Acute Flaccid Myelitis (AFM) and Guillain-Barre-Syndrome (GBS) can be challenging. [Helfferich, 2021]
  • Both typically have: [Helfferich, 2021]
    • Rapidly progressive flaccid limb weakness
    • Decreased Deep Tendon Reflexes
    • A prodromal viral prodrome
    • Monophasic course
    • MRI with nerve root enhancement
  • While there is overlap in clinical presentation, there are distinguishing features: [Helfferich, 2021]
    • AFM may have:
      • Progression stops over days
      • Asymmetric weakness
      • No sensory symptoms
      • CSF pleocytosis
      • Spinal Cord and Brain Stem Lesions on MRI
    • GBS may have:
      • Progression continues for 1-2 weeks
      • Symmetric weakness
      • Sensory symptoms present (unless pure motor GBS)
      • Deymelinating polyneuropathy on EMG
  • Some cases will fulfill clinical and diagnostic criteria for both AFM and GBS. [Helfferich, 2021]

Acute Flaccid Myelitis: Evaluation & Management

    • Obviously, in the ED, we may not get the final diagnosis determined, but we must consider it if the presentation warrants it.
    • Recent viral URI or GI symptoms should be inquired about.
    • Need to be monitored CLOSELY for progressive weakness and any respiratory difficulties.
  • Check DTRs and Strength!
    • I know… I know… we all just want to ultrasound or CT everything… but a physical exam can be useful too!
    • Don’t overlook the Cranial Nerves also!
  • MRI is the imaging modality of choice. [Vawter-Lee, 2021]
    • Gray Matter lesions in the anterior horn (predominantly)
    • Some cases may have lesions noted in the brain as well.
  • Labs: [Vawter-Lee, 2021]
    • An Acute Flaccid Myelitis Protocol has been suggested and includes various labs that may prove to help eliminate other diagnoses.
      • May defer lab results until MRI findings are known, unless imaging is to be “delayed.”
    • Blood
      • CBC, CMP
      • Arbovirus Panel (including West Nile antibodies)
      • Enterovirus PCR
      • Aquaporin-4 antibody
      • Anti-MOG antibody
      • 1 tube to send to the CDC
    • CSF
      • Cell Count, Glucose, Protein, Culture
      • Oligoclonal bands, IgG index, Meaning-encephalitis panel (viral panel)
      • Aquaporin-4 antibody
      • 1 extra mL for the CDC
    • Stool and Respiratory swabs
    • Lyme Disease, Cat Scratch, Rocky Mountain Spotted Fever evaluations also reasonable.
  • Call your Friendly Neighborhood Pediatric Neurologist! [Vawter-Lee, 2021]
  • REPORT TO THE CDC – click here for that.

Moral of the Morsel

  • Never say “It’s Just a Virus.” Viruses have always been able to do terrible things.
  • Do not be so quick to dismiss those “odd neuro complaints.” Consider Acute Flaccid Myelitis and ask more questions.
  • Check those DTRs and Strength of all Muscle groups. Sometimes proximal muscle weakness may not be appreciated until you ask the child to get out of bed!
  • Impress your Neuro Friends with your knowledge of how to distinguish between AFM and GBS. Why? Because you are a BOSS!



Sean M. Fox
Sean M. Fox
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