Acute flaccid paralysis is used as a term for a number of different conditions characterized by paralysis, including Guillain-Barré syndrome and polio. Acute flaccid paralysis is characterized clinically by the acute onset of flaccid limb weakness. Objective studies are also necessary for the diagnosis: either a magnetic resonance imaging (MRI) study which demonstrates a spinal cord lesion largely confined to the gray matter, or a cerebrospinal fluid (CSF) study with >5 white blood cells (WBCs)/mm3. Of note, the MRI might be false-positive for AFM in the first 72 hours after the onset of symptoms. All suspected cases of AFM should be evaluated for polio with a thorough vaccine and travel history, along with stool testing for polio.
There is growing concern about a spike in cases among US children of AFM -- a rare condition that causes a polio-like paralysis characterized by sudden weakness or loss of muscle tone in the arms or legs.
As of November 2, the CDC has received reports of 219 patients under investigation for AFM in 25 states, of which 80 cases have been confirmed as AFM. The average age of confirmed cases is about 4 years old.
"The case count reported today is a substantially larger number than in previous months this year," Nancy Messonnier, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, noted during a media briefing. "With enhanced efforts and working with state and local health departments and hospitals, we were able to confirm a number of new, suspected cases faster," she explained.
Going forward, the CDC announced today that it will report updated case counts every Monday afternoon on their website[https://www.cdc.gov/acute-flaccid-myelitis/afm-surveillance.html].
The CDC has been actively investigating AFM, testing specimens, and monitoring the disease since 2014, when an increase in cases was first detected. In 2014, there were 120 confirmed cases in 34 states, and in 2016, 149 confirmed cases in 39 states.
So far, in 2018, said Dr Messonnier, "we are generally on track to have the number of cases similar to what we saw in 2014 and 2016 but it would be premature to say that we are confident that we know what is going to happen because we are early in this."
According to previous years, as well as in 2018, most AFM cases occur in the late summer and fall.
Dr Messonnier emphasized that AFM remains "incredibly rare. Overall, the rate over the years that it's been diagnosed since 2014 is less than one in 1 million."
Dr Messonnier said it remains unclear what causes AFM. "We know that poliovirus is not the cause of these cases. [The] CDC has tested every stool specimen from AFM patients. None of the specimens has tested positive for poliovirus," she said. AFM may be caused by other viruses, environmental toxins, or genetic disorders.
"There is a lot we don't know about AFM, and I am frustrated that despite all of our efforts we have not been able to identify a cause of this mystery illness," said Dr Messonnier. "Despite extensive laboratory testing, we have not determined what pathogen or immune response causes the arm or leg weakness or paralysis in most of these patients. We don't know who may be at higher risk for developing AFM or the reasons why they may be at higher risk," she added.
"We also don't fully understand what the long-term consequences of AFM are or why some patients diagnosed with AFM have recovered quickly while others continue to have paralysis and require ongoing care," said Dr Messonnier.
The CDC has developed a tool kit for healthcare professionals that includes information about AFM and instructions for reporting patients under investigation to the health department.
AFM was first noted in the United States during 2014, when it caused 120 confirmed cases in 34 states.
In 2015, the number of AFM cases dropped to 22, but it rose again to 149 patients in 2016.
2017 was another slow year for AFM, with a total of 33 confirmed cases; however, 80 cases of AFM have been confirmed so far in 2018, with another 111 cases under review.
Most cases have occurred among children, and symptoms have been similar to infections with polio and nonpolio enterovirus, adenoviruses, and West Nile virus.
Still, no common pathogen has been isolated from the CSF of patients with AFM, leaving the principal causative agent a mystery.
Cases have occurred most commonly in the late summer and early fall.
Patients with AFM may also demonstrate facial droop or difficulty with swallowing or speech.
Numbness or tingling is rare in AFM, although some patients complain of pain in their arms or legs.
Respiratory failure in AFM can lead to the need for urgent ventilator support.
The long-term prognosis of AFM is not known.
The CDC recommends general approaches for the prevention of AFM, including complete vaccination against polio and mosquito control measures to reduce transmission of the West Nile virus.
The statement also mentions that environmental toxins could possibly play a role in the pathophysiology of AFM.
AFM is defined by the acute onset of flaccid paralysis of a limb along with either MRI or CSF findings plus the absence of a known cause of flaccid paralysis such as polio.
The prevalence of AFM is very low overall in the United States, but it has been variable over the past 4 years. It is most common in the late summer and early fall and primarily affects children. As yet, the precise cause of AFM is unknown, as is its long-term prognosis.
Implications for the Healthcare Team: The healthcare team is limited in what it can do to prevent or treat AFM, but they should remain vigilant for the symptoms of AFM and also assuage worried parents whose children do not have AFM.