A mystery illness that leaves children barely able to move is making a comeback, two years after an outbreak alarmed doctors and parents.  Acute flaccid myelitis (AFM) is a rare illness that anyone can get. It affects a person’s nervous system, specifically the spinal cord. AFM can result from a variety of causes, including viral infections:

• enteroviruses (polio and non-polio),
• West Nile virus (WNV) and viruses in the same family as WNV, specifically Japanese encephalitis virus and Saint Louis encephalitis virus, and
• adenoviruses.

AFM is one of a number of conditions that can result in neurologic illness with limb weakness. Such illnesses can result from a variety of causes, including viral infections, environmental toxins, genetic disorders, and Guillain-Barre syndrome, a neurologic disorder caused by an abnormal immune response that attacks the body’s nerves. Oftentimes, however, despite extensive laboratory testing, a cause for AFM is unable to be identified

Most patients will have sudden onset of limb weakness and loss of muscle tone and reflexes. Some patients, in addition to the limb weakness, will experience:

• facial droop/weakness,
• difficulty moving the eyes,
• drooping eyelids, or
• difficulty with swallowing or slurred speech.

Numbness or tingling is rare in patients with AFM, though some patients have pain in their arms or legs. Some patients with AFM may be unable to pass urine. The most severe symptom of AFM is respiratory failure that can happen when the muscles involved with breathing become weak. This can require urgent ventilator support (breathing machines).

In June 2015, the Council of State and Territorial Epidemiologists (CSTE) adopted a standardized case definition for acute flaccid myelitis[6 pages]. As of August 1, 2015, a patient must meet the clinical criteria below to be considered either a confirmed or probable case of acute flaccid myelitis:

Confirmed Cases

To be considered a confirmed case, a patient must meet the following criteria:

1. Acute onset of focal limb weakness, AND
2. An MRI showing a spinal cord lesion largely restricted to gray matter and spanning one or more spinal segments.

Probable Cases

To be considered a probable case, a patient must meet the following criteria:

1. Acute onset of focal limb weakness, AND
2. Cerebrospinal fluid (CSF) with pleocytosis (white blood cell count >5 cells/mm³, adjusting for presence of red blood cells by subtracting 1 white blood cell for every 500 red blood cells present).

Source: Mystery illness that paralyzes children on the rise again