Clinical Overview of AFM

Introduction

The term acute flaccid myelitis was created in fall of 2014 to describe patients with sudden onset of acute flaccid limb weakness without a known cause and with lesions in gray matter of the spinal cord. There can be some white matter involvement. Most cases are in children.

Viral causes include:

• Non-polio enteroviruses (EV-D68, EV-A71)
• Flaviviruses (West Nile virus, Japanese encephalitis virus)
• Herpesviruses
• Adenoviruses

Clinical presentation is similar to poliomyelitis, but poliovirus has not been detected in any specimens from patients with AFM.

Cause

Viral causes include:

• Non-polio enteroviruses (EV-D68, EV-A71)
• Flaviviruses (West Nile virus, Japanese encephalitis virus)
• Herpesviruses
• Adenoviruses

Clinical presentation is similar to poliomyelitis, but poliovirus has not been detected in any specimens from patients with AFM.

Clinical features

Most patients had preceding febrile illness 1–2 weeks before onset of acute flaccid limb weakness.

• Frequently respiratory or gastrointestinal illness (GI) with symptoms of fever, rhinorrhea, cough, vomiting or diarrhea.
• Onset of weakness is rapid, within hours to a few days.
• Weakness is in one or more limbs and is more proximal than distal.
• Loss of muscle tone and reflexes in the affected limb(s).

Cranial nerve abnormalities can be present:

• Facial or eyelid droop
• Difficulty swallowing or speaking
• Hoarse or weak cry

Some patients might complain about stiff neck, headache, or pain in the affected limb(s).

In uncommon cases, people can also have numbness or tingling.

The most severe symptoms of AFM are:

• Respiratory failure, requiring mechanical ventilation
• Serious neurologic complications such as body temperature changes and blood pressure instability that could be life threatening

Differential Diagnosis of Flaccid Limb Weakness

AFM can resemble:

• Synovitis
• Neuritis
• Limb injury
• Guillain-Barre syndrome (GBS)
• Transverse myelitis
• Stroke, including spinal stroke
• Tumor
• Acute cord compression
• Conversion disorder

AFM must be high on differential diagnosis in late summer or early fall, especially in patients with preceding viral symptoms.

Careful neurological examination, laboratory testing, and MRI of the spine and brain can help guide diagnosis.

Testing and diagnosis

During the initial evaluation for AFM: collect patient's medical history, perform a physical exam along with an age-appropriate neurological assessment, and ask questions to evaluate limb function impairment.

Collect the patient's medical history

• Collect information on any illness in the past 4 weeks
• Note respiratory and GI symptoms, with or without fever
• Ask about hand, foot, and mouth lesions (possible EV-A71 or similar viral infection)

Physical Exam

Perform physical exam along with an age-appropriate neurological assessment and ask questions to evaluate limb function impairment.

Neurological examination should include documentation of:

• Muscle tone (flaccid/loose vs spastic/tight and firm)
• Muscle strength (full strength, move against gravity with some resistance/pressure, move against gravity but with no resistance/pressure, or little limb movement but not against gravity, no muscle movement at all)
• Reflexes in each extremity (hypo-, hyper, or absent)
• Any cranial nerve deficiencies such as for facial, palatal and shoulder asymmetry, hoarseness or hypophonia and dysphagia (if possible)

Note: Sensory exam is often normal in patients with AFM.

Assess the patient's ability to protect their airway:

• Document respiratory sufficiency
• Negative inspiratory force may be used if the child is old enough and able to cooperate

Check for autonomic manifestations:

• Blood pressure lability
• Body temperature instability

Ask about additional signs and symptoms, including:

• Difficulty holding their head up
• Decreased appetite or difficulty swallowing
• Increased sleepiness or inactivity
• Headache or neck, shoulder, or back pain
  • Patients often complain of this prior or concurrent to weakness
• Pain in extremities
• Bowel or bladder changes, particularly constipation

Examining proximal muscle weakness

When examining patients with sudden limb, neck, or trunk weakness, remember to check both proximal and distal muscle strength, as impairment in proximal strength can be easily missed during exams.

Keep in mind that young children or their parents may not describe their limb function impairment as "weakness."

Diagnostic Studies for AFM

Careful neurological examination, laboratory testing, and MRI of the spine and brain can help guide diagnosis. Specific testing for AFM should be done in consultation with a neurologist and infectious disease specialists.

Patient management

CDC provides clinical guidance based upon the review of available scientific literature on AFM and individual input from subject matter experts. Clinicians should immediately consult with their local neurologists and/or infectious disease specialists for treatment and medical management decisions for any suspected AFM patient.

What CDC is doing

Read more about what CDC is doing to research and learn more about AFM.

Case definitions

A person with illness that meets clinical AND laboratory/imaging criteria for reporting should be considered a possible AFM case and should be reported to the health department.