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What is Acute Flaccid Myelitis?

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Acute Flaccid Myelitis (AFM) is inflammation of the spinal cord that causes sudden muscle weakness. It is a  rare condition and less than a million new cases are recorded annually from all over the world. It chiefly affects children. AFM causes damage to the gray matter of the spinal cord, where the cell bodies of neurons are located. This affects the ability to pass signals between the central and peripheral nervous system.

AFM disease or acute flaccid myelitis medical concept as a neurologic condition representing enterovirus or polio virus as a 3D illustration. Image Credit: Lightspring / Shutterstock
AFM disease or acute flaccid myelitis medical concept as a neurologic condition representing enterovirus or polio virus as a 3D illustration. Image Credit: Lightspring / Shutterstock

Signs and Symptoms

Symptoms of AFM are similar to those of poliomyelitis. Children affected by AFM experience acute weakness of the muscles (myotonia), including the muscles of the arms, legs, face, mouth and the eye. The onset of muscle weakness is sudden and some patients report pain. The most common symptoms in children with AFM include:

  • acute onset of weakness of muscles in the arms or legs
  • loss of muscle reflexes
  • facial muscle palsy, including drooping eyelids
  • difficulty with ocular movement
  • difficulty with swallowing
  • slurring of speech

Some less common symptoms include tingling and numbness in the arms and legs, as well problems in the passage of urine. The symptom intensity depends on the localization and number of neurons damaged, and complete paralysis may occur in the most severe cases. AFM is most dangerous when the respiratory muscles are affected, as this may cause respiratory failure.

If AFM is caused by a preceding viral infection, the length of time between infection and the occurrence of the earliest symptoms depends on the type of virus. As AFM is considered a rare disease, the symptoms may also vary on a case-to-case basis.

Causes

AFM is known to cause polio-like symptoms. However, while it can be caused by the polio virus, other causes include:

  • Environmental factors
  • Autoimmune disorders
  • Viruses, including the West Nile virus and enteroviruses

Among enteroviruses, the enterovirus D68 in particular is associated with the onset of AFM. Recent studies have shown that current circulating enterovirus D68 strains have acquired the capacity for viral entry and replication in human neuronal cells. An outbreak of enterovirus D68 in the United States in 2014 was concurrent with a rise in pediatric cases of AFM and in 2016, there were 29 recorded cases of AFM associated with this virus in Europe.

In many cases, however, the cause for the condition is not easily determined. Furthermore, even when the primary cause is a viral infection, the exact pathological mechanism underlying the development of AFM is not known. Some patients with a particular viral infection go on to develop AFM while others do not. Thus one subject of ongoing study is to identify the root reason for this difference.

Diagnosis

AFM is generally diagnosed by an MRI scan that reveals degradation of the gray matter of the spinal cord. Early diagnosis is important as it may increase the availability and effectiveness of treatment. When diagnosing AFM, it is important to differentiate it from other conditions that it may be similar to, which makes it difficult to diagnose. This includes:

  • Guillain-Barre syndrome (GBS)
  • transverse myelitis
  • acute disseminated encephalomyelitis (ADEM)

A physical examination may aid in arriving at the right diagnosis. Other tests include:

  • testing the content of cerebral spinal fluid (CSF)
  • nerve conduction velocity (NCV) tests
  • electromyography (EMG) to test muscle response to stimuli from nerve cells
  • Respiratory PCR panel, enterovirus PCR
  • West Nile Virus IgG and IgM in serum, EBV antibodies, Lyme serology (where applicable), enterovirus PCR

Treatment

In a few cases of AFM, children recover fully. However, in other cases there are lasting effects. No established treatment options are currently available for AFM. Depending on the case and severity, some possible treatment options include:

  • Intravenous immunoglobulin (IVIG) treatment
  • Corticosteroids
  • Plasma exchange
  • Physical and occupational therapy

While no vaccination is currently available against the enterovirus 68, the polio virus vaccine is recommended to avoid a condition very similar to AFM. Good hygiene practices are also essential to prevent infection with the West Nile virus that spreads through mosquito bites.  Physical therapy and occupational therapy are particularly important during recovery, as they promote muscle growth and regeneration.

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