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Acute Flaccid Myelitis – Could You Make the Diagnosis?

November 24, 2018

Written by Clay Smith

Spoon Feed
There has been a surge of acute flaccid myelitis (AFM) cases this year, similar to poliomyelitis. The etiology is unknown. Here is how to recognize and treat it based on what we know at this point.

Why does this matter?
If someone or their child has sudden onset weakness, where will they come? They will come to the ED. We need to be aware of this clinical presentation and know how to recognize and manage it.

Don’t be weak – learn about acute flaccid myelitis

Clinical Presentation

  • Here is the standard case definition.

  • It is similar to poliomyelitis.

  • There is rapid onset of flaccid weakness in one or more limbs over hours to days.

  • “Cranial nerve abnormalities, resulting in facial weakness, ophthalmoplegia, and bulbar signs such as dysarthria and dysphagia, may be variably present.”

  • This year, 99% of confirmed cases had a viral illness (respiratory or, less often, GI) or fever (81%) in the 4 weeks prior to onset of weakness.

  • MRI shows characteristic spinal cord gray matter edema, predominantly affecting the anterior horn or central cord; “also notable signal abnormality and enhancement of ventral nerve roots in some patients, as well as variable lesions noted in the brainstem, particularly the dorsal pons.”

  • CSF pleocytosis with >5 WBCs is often seen. But there is no, “cytoalbuminologic dissociation (elevated CSF protein in the absence of pleocytosis) as seen in Guillain Barré syndrome.”


“Report any illness to public health authorities that meets all of the following criteria:

  • A person with onset of acute flaccid limb weakness, AND

  • A magnetic resonance image showing a spinal cord lesion largely restricted to gray matter*†, and spanning one or more vertebral segments OR Cerebrospinal fluid (CSF) with pleocytosis (CSF white blood cell count >5 cells/mm3); CSF protein may or may not be elevated”

* Spinal cord lesions may not be present on initial MRI; a negative or normal MRI performed within the first 72 hours after onset of limb weakness does not rule out AFM. MRI studies performed 72 hours or more after onset should also be reviewed if available.

† Terms in the spinal cord MRI report such as “affecting mostly gray matter,” “affecting the anterior horn or anterior horn cells,” “affecting the central cord,” “anterior myelitis,” or “poliomyelitis” would all be consistent with this terminology.


  • See this for Interim Considerations for Clinical Management.

  • The cause is unknown and not confirmed to be related to enterovirus (EV-D68).

  • Consider other causes of weakness, such as herpes simplex virus neurologic infection, CNS bacterial infection, or Guillain-Barre syndrome.

  • Be alert for exacerbation of chronic medical conditions from the fever or weakness, such as asthma or diabetes mellitus.

  • Admit to the ICU if:

    • Respiratory muscle weakness on exam

    • Hypoxia/hypercarbia

    • Vital capacity < 15 mL/kg | negative inspiratory force (NIF) < 30 cmH2O

    • Impaired airway protection due to bulbar weakness, altered mental status, or autonomic instability

    • Cervical lesion on MRI

    • Rapidly progressive course

  • “Summary of Interim Considerations

    • a. General routine clinical management of children with AFM should adhere to basic standards of care for children with severe neurologic disease.

    • b. Physical and occupational therapy should be implemented as soon as the child is physically stable in order to optimize functional outcomes.

    • c. There are currently NO targeted therapies / interventions that are felt to have definitive efficacy in the treatment or management of AFM. Reviewing numerous possible targeted interventions, the experts found no concrete evidence for indication of corticosteroids, IVIG, plasmapheresis, interferon, antivirals, or other immunomodulatory agents in the treatment of AFM.

    • d. Plasmapheresis and immunosuppressive biologic modifiers, including corticosteroids, should be discouraged in the management of AFM.

    • e. The considerations for management described in this document will be revised as needed if more information becomes available.”

Another Spoonful
There was a new MMWR update on AFM last week. This new info is included above.


What are your thoughts?