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Why You Should Think Acute Flaccid Myelitis, Not Just Polio
The Signs and Symptoms to Look for

Article In Brief

Despite a recent case of paralytic polio in New York state and evidence of community transmission of the virus, experts point out that other causes, such as enteroviruses and West Nile virus, could be behind patients' symptoms.

A case of poliomyelitis in New York state suddenly has people talking about polio, but experts say clinicians should first think about the broader category of acute flaccid myelitis (AFM) when evaluating a patient with a sudden onset of lower limb weakness.

The case of paralytic polio was identified in July in an unvaccinated young adult in Rockland County, NY, making it the first case of wild polio originating in the US since 1979. Poliovirus has also been detected in wastewater samples collected from New York City and nearby Rockland and Orange counties, as well as Sullivan County and Nassau County, suggesting there is community transmission of the virus and ongoing risk for paralytic polio for other unvaccinated people.

At press time, New York Gov. Kathy Hochul declared a state disaster emergency to increase resources and the network of polio vaccine administrators.

“We're in an era where there are these infectious diseases that ‘modern’ physicians have only read about in textbooks,” said James Sejvar, MD, FAAN, a neuroepidemiologist with the division of high-consequence pathogens and pathology at the Centers for Disease Control and Prevention (CDC).

“It is concerning and a public health challenge,” Dr. Sejvar said of the reemergence of a once dreaded disease that was declared eradicated in the US in 1994. But he does not expect that polio will cause widespread outbreaks of disease here, given the availability of vaccines and wastewater surveillance systems that can signal the possibility of community spread.

“But it does serve as another stark reminder that vaccinations are critical and vaccination campaigns are important,” Dr. Sejvar said.

Kevin Messacar, MD, PhD, a pediatric infectious diseases researcher at Colorado Children's Hospital and University of Colorado, said the polio case in New York should also alert clinicians to the possibility of AFM in general, which can be caused by multiple viruses, including poliovirus, other enteroviruses, and West Nile virus. The US experienced biennial outbreaks in recent years of an enterovirus called EV-D68, which causes respiratory illness and sometimes serious paralysis in children, and cases are cropping up this fall.

The New York polio case came amid worrying signs of a decline in overall childhood vaccination rates in the US, much of it attributed to people putting off routine health care visits during the COVID-19 pandemic.

According to the CDC's August 19 Morbidity and Mortality Weekly Report (MMWR), New York state immunization data indicate that the three-dose polio vaccination coverage for infants and children under 24 months of age in Rockland County declined from 67 percent in July 2020 to 60.3 percent in August 2022. In some communities, the vaccination rate was as low as 37.3 percent.

The polio case in New York involved an immunocompetent adult who went to an emergency department with a five-day history of low-grade fever, neck stiffness, back and abdominal pain, constipation, and two days of bilateral lower extremity weakness, according to the MMWR report. He was hospitalized with suspected AFM, and then diagnosed with polio based on stool samples that tested positive for poliovirus type 2.

Genetic sequencing indicated that the polio infection was due to community spread involving a chain of transmission that likely started with someone who had received the type-2 containing oral polio vaccine (OPV) abroad. (Inactivated polio vaccine, IPV, is given in the US.) The patient with polio, who was sent to a rehabilitation center with ongoing lower extremity flaccid weakness 16 days after symptoms started, had not travelled internationally during the presumed incubation period for poliovirus. The genetic sequencing revealed a link to type-2 poliovirus detected in wastewater in Israel, where a patient with polio was identified in Jerusalem in February, and the United Kingdom.

Dr. Sejvar said that federal, state, and local health officials used the National Wastewater Surveillance System, which was put in place in 2020 to monitor the spread of SARS-CoV-2 in wastewater, to look for signs of poliovirus circulating in the Rockland County area. The surveillance indicated community spread.

Dr. Sejvar said three other potential polio cases from the Rockland County area were placed under investigation by health officials in late summer but testing for poliovirus in various biological samples were negative and polio was ruled out.

“Replication of OPV in a person who was recently vaccinated can result in viral reversion to neurovirulence, which can cause paralytic poliomyelitis in unvaccinated persons who are exposed to the vaccine-derived virus,” the MMWR report said. “Until poliovirus eradication is achieved worldwide, importations of both wild polioviruses and VDPVs [vaccine-derived polioviruses] into the United States are possible.”

Health workers worldwide have strived for years to eradicate polio globally through vaccination campaigns, but polio type-1 is still considered endemic in Afghanistan and Pakistan, and periodic outbreaks occur in dozens of countries, mostly in Asia and Africa.

Raymond P. Roos, MD, FAAN, the Marjorie and Robert E. Straus Professor in Neurological Science in the department of neurology at University of Chicago, said many clinicians in this country may have to reacquaint themselves with the signs and symptoms of polio and how to diagnose it. There is no treatment besides symptom management and supportive care, he said, while stressing that the polio vaccine prevents serious problems in the first place.

“My guess is that you would have a hard time finding physicians in the US who have seen acute polio,” Dr. Roos said.

Signs and Symptoms

Most people infected with poliovirus have no obvious symptoms or have only mild flu-like symptoms such as sore throat, fever, fatigue, and nausea. A small proportion of infected persons will experience potentially life-threatening symptoms such as meningitis—which occurs in about one in 25 infected persons—and paralysis—which affects about one in 200 infected persons—due to the virus invading the brain and spinal cord. While many people recover, there can be permanent paralysis of the arms and legs. Another concern involves the possibility of a condition called post-polio syndrome, with progressive muscle weakness and disability developing sometimes decades after recovery.

Dr. Roos said that AFM in general, and polio specifically, may look a lot like Guillain-Barré syndrome (GBS), which is caused by inflammation of the peripheral nerves. Typical presentations include acute and sometimes progressive weakness in the lower limbs with or without paralysis, muscle tenderness, and perhaps trouble swallowing or breathing.

“Other viruses can cause diseases that look like polio. Fortunately, we have diagnostic tests that can usually identify the specific disease and cause, such as a spinal fluid exam and polymerase chain reaction (PCR),” Dr. Roos said.

According to the CDC, polio-related “paralysis usually begins in the arm or leg on one side of the body (asymmetric) and then moves towards the end of the arm or leg,” progressing to involve distal muscle groups.

“Clinicians need to first make sure they are ruling out other common causes of paralysis such as GBS,” said Carlos Pardo-Villamizar, MD, professor of neurology at Johns Hopkins University School of Medicine. ?Although polio and GBS present with weakness, GBS cases are frequently associated also with sensory symptoms while polio does not, he said. MRI helps to establish the diagnosis of AFM or eventually poliomyelitis.

Dr. Pardo-Villamizar heads the Acute Flaccid Myelitis Working Group, a consortium of doctors and scientists focused on AFM, which recently posted two podcasts on YouTube on polio in response to the New York case: and

According to the CDC, assessing for poliovirus includes testing of stool, pharyngeal swabs, and blood and cerebrospinal fluid samples, though the virus is rarely detected in blood or spinal fluid.

“Neurologists need to be alert,” Dr. Pardo-Villamizar said, but also must keep in mind that a case of AFM in the US is more likely to be caused by viruses other than poliovirus, such as West Nile virus or enterovirus D68. “I don't think we don't need to alarm parents,” he said. “But we do need to say, ‘Hey parents, we won't have to deal with polio if everyone is vaccinated.’”

Health Officials and Infectious Disease Doctors

The need to now focus on an old virus, poliovirus, comes amid nearly three years of intense attention to a new virus, SARS-CoV-2, which causes COVID-19 and is responsible for more than one million deaths in the US alone.

Kiran Thakur, MD, a neuroinfectious diseases specialist and neurohospitalist at Columbia University Irving Medical Center-New York Presbyterian Hospital, said the case, while troubling, needs to be kept in perspective.

“For clinicians, what I think we need to emphasize is that paralytic polio remains extremely rare and that overall, most of the population has been vaccinated when they were children or young adults,” she said. “This is a vaccine success story—that it (the polio vaccine) is highly effective in preventing the neurologic compilations of poliovirus.”

As for lagging vaccination rates in recent years, she said COVID-19 may be partly to blame but she noted that “there are also pockets of the community that have been targeted by anti-vaccine campaigns and historically vulnerable communities have low vaccine rates that have nothing to do with COVID.”

Personal details of the Rockland County case and why the person was not vaccinated against polo have not been made public due to standard privacy issues.

Dr. Thakur stressed that clinicians evaluating a patient with polio-like symptoms need to quickly include a vaccination history. One should consider other conditions that may have similar clinical symptoms and radiologic features, she said, including other viral causes of acute flaccid myelitis (for example enterovirus D68, West Nile virus) and conditions which may present similarly including GBS.

An MRI of the spinal cord should be done in those individuals who have signs concerning for anterior horn cell disease, and early collection of biologic samples including stool, CSF and respiratory samples, according to CDC guidance, may lead to etiological diagnosis, she said.

Dr. Thakur said it is important for clinicians to reach out to public health officials and infectious disease specialists early on when evaluating a potential polio case. The New York case was “identified and reported through the AFM surveillance system,” a national surveillance system started by the CDC in 2014 due to an increase in AFM cases predominantly seen in children.

Dr. Messacar said doctors should be particularly suspicious of possible AFM caused by EV-D68 or A-71 in children in the months ahead because the enteroviruses are starting to pop up around the country. EV-D68, for which there is no vaccine, has caused illness in the US every two years since 2014, typically late summer and fall, though cases were minimal during the height if the COVID-19 pandemic, likely because many children weren't in school or daycare, he said.

“We have not seen an uptick since 2018,” said Dr. Messacar, and he and other infectious disease experts worry that the virus may hit especially hard this fall. “There are now four years of children who haven't been exposed to those viruses and may have less immunity,” he said.

“I think we need to have a heightened suspicion for AFM at this time of year regardless of what the cause is,” Dr. Messacar said, noting that the recommended diagnostic workup for AFM is the same no matter the specific pathogen involved.

The CDC issued a health alert on Sept. 9 advising health care providers that there could be an increase in AFM cases in the coming weeks. The agency said there are more children hospitalized with severe respiratory who tested positive for rhinovirus and/or enterovirus, in particular, EV-D68.

Editor's Note: At Neurology Today, we shy away from publishing obituaries. But when we lose someone from our editorial family, we make an exception—as we do here in noting the sudden death in September of one of our longest contributing writers, Kurt Samson. Although Kurt's byline had neither a medical nor doctoral degree, he brought a natural curiosity and passion for reporting on all things related to the brain. He wrote about an exhaustive range of subjects with clarity and balance—from the most basic neuroscience to complex and controversial policies impacting neurologists. His articles won national editorial awards. His loss leaves a deep hole, and we will miss him.

Link Up for More Information

• Link-Gellis R, Lutterloh E, Ruppert PS, et al; for the Poliovirus Response Team. Public health response to a case of paralytic poliomyelitis in an unvaccinated person and detection of poliovirus in wastewater—New York, June-August 2022 MMWR Morb Mortal Wkly Rep 2022;71(33):1065–1068.
• CDC resource on polio: Accessed September 9, 2022.