Acute Flaccid Myelitis (AFM): Understanding the “Polio-like” Illness Affecting the Spinal Cord
Acute flaccid myelitis (AFM) is a rare but serious neurological disorder that primarily affects children and results in sudden weakness or paralysis in the limbs. Often referred to as a “polio-like” illness, AFM has drawn growing attention over the past decade due to its similarities with poliomyelitis and its seasonal spikes in reported cases.
While AFM remains uncommon, its potential severity—and the uncertainty surrounding its causes—make it an important condition for clinicians, parents, and public health officials to understand.
What Is Acute Flaccid Myelitis?
AFM is a condition that affects the gray matter of the spinal cord, where it damages motor neurons responsible for muscle movement. This leads to acute, flaccid paralysis, meaning muscles become limp and weak, often without warning. The condition can progress rapidly, and in some cases, the weakness can become long-lasting or even permanent.
Although its symptoms resemble those of poliovirus infection, AFM is not caused by the poliovirus. Instead, it appears to be associated with other viral pathogens, many of which circulate widely but only rarely cause such severe neurological effects.
Key Characteristics of AFM
1. Sudden Onset of Limb Weakness
AFM typically begins with the sudden appearance of weakness in one or more limbs. The weakness is often asymmetrical and may progress over hours to days. Affected individuals may also lose reflexes and muscle tone in the impacted limbs.
2. Neurological Damage
The hallmark of AFM is inflammation and damage in the spinal cord’s gray matter, particularly in the anterior horn cells—the same neurons targeted by the poliovirus. This neuronal damage disrupts communication between the brain and muscles, resulting in the observed weakness and paralysis.
Signs and Symptoms
AFM may begin with general viral symptoms such as fever, cough, or sore throat, but neurological symptoms typically follow within a few days. These include:
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Sudden weakness in the arms or legs
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Decreased or absent reflexes
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Loss of muscle tone
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Facial weakness or drooping
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Difficulty moving the eyes or swallowing
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Slurred speech
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In severe cases, difficulty breathing due to paralysis of respiratory muscles
What Causes AFM?
Although the exact cause of AFM is not always confirmed in each case, increasing evidence points to a strong link between AFM and viral infections. Key suspected and confirmed viral triggers include:
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Enteroviruses: Especially EV-D68 and EV-A71, which have been detected in many AFM patients.
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Flaviviruses: Such as West Nile virus and Japanese encephalitis virus.
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Herpesviruses: Including herpes simplex virus and human herpesvirus 6 (HHV-6).
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Adenoviruses: Common respiratory viruses that may occasionally contribute to AFM.
It’s believed that these viruses may either directly infect spinal cord neurons or trigger an abnormal immune response that damages the nervous system.
Source: CDC – Causes of AFM
https://www.cdc.gov/acute-flaccid-myelitis/causes/index.html
How Is AFM Diagnosed?
Prompt and accurate diagnosis is essential. Diagnosis usually includes:
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Detailed medical history and symptom review
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Neurological examination
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MRI of the spinal cord, which typically shows lesions in the gray matter
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Lumbar puncture (spinal tap) to analyze cerebrospinal fluid (CSF)
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Laboratory testing for viruses in respiratory specimens, stool, or CSF
Because AFM progresses quickly and can resemble other neurological disorders, early recognition is critical to avoid misdiagnosis and to begin supportive treatment as soon as possible.
Treatment and Management
There is currently no specific antiviral treatment or cure for AFM. Instead, care focuses on managing symptoms and preserving function. Treatment strategies may include:
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Supportive care such as pain management and respiratory support (including mechanical ventilation if needed)
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Physical and occupational therapy to improve strength, coordination, and mobility
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Rehabilitation programs tailored to the patient’s specific neurological deficits
Experimental treatments, such as intravenous immunoglobulin (IVIG), corticosteroids, or plasmapheresis, have been tried in some cases, but their effectiveness remains unclear and is still under investigation.
Long-Term Outlook and Complications
Outcomes vary. Some patients experience significant improvement over time, especially with early and intensive rehabilitation. However, others may have persistent weakness, paralysis, or other complications such as:
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Chronic pain
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Reduced mobility
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Difficulty breathing or swallowing
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Emotional or psychological challenges
In severe cases, especially those affecting respiratory muscles, AFM can be life-threatening.
Prevalence and Seasonal Patterns
AFM is a rare condition, but its incidence has increased in recent years. In the United States, the Centers for Disease Control and Prevention (CDC) began actively tracking AFM in 2014, following a notable uptick in pediatric cases.
Notably, AFM tends to follow a biennial pattern, with cases peaking every two to four years, typically in late summer and early fall—a pattern that correlates with seasonal outbreaks of certain enteroviruses.
Conclusion
Although acute flaccid myelitis is rare, its potential for rapid progression and lasting impact makes it a condition of growing concern, especially in children. While the exact mechanisms remain under study, AFM appears to be linked to viral infections that are otherwise common and mild in most people.
Ongoing research is crucial to identifying effective treatments and preventive strategies. Meanwhile, heightened awareness, early diagnosis, and supportive care remain the best tools available to reduce the long-term effects of this mysterious and serious neurological illness.
References:
What causes acute flaccid myelitis? https://www.cdc.gov/acute-flaccid-myelitis/causes/index.html
And https://www.chop.edu/conditions-diseases/acute-flaccid-myelitis-afm
And https://medlineplus.gov/acuteflaccidmyelitis.html
© 2000-2025 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a fife year copy right. Library of Congress Card Number: LCN 00-192742
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