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Disease Profile

Acute flaccid myelitis

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


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Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable



Acute flaccid myelitis (AFM) is a condition that affects the spinal cord leading to muscle weakness and loss of reflexes. Most people who develop AFM have had a viral illness with flu-like symptoms one to four weeks before symptoms of AFM. Symptoms of AFM include sudden onset (acute) of weakness in the arm(s) or leg(s), loss of muscle tone, and decreased or absent reflexes. Other symptoms may include pain, facial weakness, and difficulty swallowing, speaking, or moving the eyes. It is not clear why some people develop AFM and others do not. Diagnosis is based on the symptoms, a clinical exam, an MRI of the spine, and other laboratory testing. Most people with AFM continue to have muscle weakness for months to years. Sometimes the muscles involved with breathing become weakened, and ventilator support is necessary to help with breathing. The long-term outcome for people with AFM is unknown. Treatment is focused on managing the symptoms and includes aggressive physical therapy.[1][2][3][4]


The following list includes the most common signs and symptoms in people with acute flaccid myelitis (AFM). These features may be different from person to person. Some people may have more symptoms than others and symptoms can range from mild to severe. This list does not include every symptom or feature that has been described in AFM.

Symptoms may include:[3]

  • Sudden onset of muscle weakness, usually in an arm or leg
  • Pain
  • Facial weakness
  • Difficulty breathing, swallowing, speaking
  • Bowel or bladder control problems

Symptoms usually occur one to four weeks after a flu-like illness (fever, cough, stomach distress). Children are more likely to be affected than adults. Muscle weakness comes on quickly and may involve one to four limbs. The arms are more likely to be affected. Sometimes the muscles involved with breathing become weak and mechanical breathing support (a ventilator) is needed. Most people who get AFM will have symptoms for months or even years. Because AFM has only recently been described, not much is known about the long-term affects of this condition.[2][4]


The cause of acute flaccid myelitis (AFM) is still unclear. Increasing evidence suggests that a type of virus known as an enterovirus is involved. Most people who get sick from an enterovirus get flu-like symptoms such as fever, cough, congestion, vomiting, and/or diarrhea. Only some of those people who get will develop AFM. It is not clear why some people who get a viral illness get AFM and it is not known how the infection triggers AFM.[2][4] 

There is no known way to prevent AFM. However, preventing a viral infection can help reduce the risk of developing AFM. Steps to preventing a viral illness include frequent hand washing, cleaning surfaces, avoiding sick people, and staying home when you are sick.[1]


The Centers for Disease Control and Prevention (CDC) has developed guidance for recognizing acute flaccid myelitis (AFM). Diagnosis is based on recognizing the symptoms. It may include a physical exam, an MRI of the spine, testing of the cerebral spinal fluid (CSF), and tests checking nerve speed (nerve conduction velocity; NCV) and the response of muscles to the messages from the nerves (electromyography; EMG).[1][2][3]

AFM can be difficult to diagnose because the symptoms are similar to other neurological diseases, such as Guillain-Barre syndrome (GBS), acute disseminated encephalomyelitis (ADEM), and transverse myelitis. These conditions may need to be excluded before the diagnosis of AFM can be made.[2]


There is no specific treatment for acute flaccid myelitis. Aggressive physical therapy may help recovery. Other treatments that have been tried include immunoglobulins, corticosteroids, plasma exchange, and antiviral therapy, but there is no clear evidence that any of these treatments changes the outcome.[3][4] 

For more detailed information about acute flaccid myelitis, visit the Centers for Disease Control and Prevention (CDC) webpage.


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

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      Learn more

      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      Where to Start

      • You can obtain information on this topic from the Centers for Disease Control and Prevention (CDC). The CDC is recognized as the lead federal agency for developing and applying disease prevention and control, environmental health, and health promotion and education activities designed to improve the health of the people of the United States.
      • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.

        In-Depth Information

        • PubMed is a searchable database of medical literature and lists journal articles that discuss Acute flaccid myelitis. Click on the link to view a sample search on this topic.

          Selected Full-Text Journal Articles


            1. Acute flaccid myelitis. Centers for Disease Control and Prevention. February 25, 2020; https://www.cdc.gov/acute-flaccid-myelitis/about-afm.html.
            2. Helfferich J, Knoester M, Van Leer-Buter CC, et al. Acute flaccid myelitis and enterovirus D68: lessons from the past and present. Eur J Pediatr. 2019;178(9):1305-1315. 2019; 178(9):1305-1315. https://pubmed.ncbi.nlm.nih.gov/31338675.
            3. Fatemi Y, Chakraborty R. Acute Flaccid Myelitis: A Clinical Overview for 2019. Mayo Clin Proc. 2019; 94(5):875-881. https://pubmed.ncbi.nlm.nih.gov/31054607.
            4. Morens DM, Folkers GK, Fauci AS. Acute Flaccid Myelitis: Something Old and Something New. mBio. 2019; 10(2):e00521-19. https://pubmed.ncbi.nlm.nih.gov/30940708.
            5. Hopkins SE. Acute Flaccid Myelitis: Etiologic Challenges, Diagnostic and Management Considerations. Curr Treat Options Neurol. November 28, 2017; 19(12):48. https://www.ncbi.nlm.nih.gov/pubmed/29181601.

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