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  • Updated 07.12.2023
  • Released 05.21.2021
  • Expires For CME 07.12.2026

Acute flaccid myelitis



Acute flaccid myelitis is a rapidly evolving anterior horn disease that clinically manifests with devastating flaccid paralysis of limbs or bulbar palsy. Pediatric populations are preferentially affected. Acute flaccid myelitis is often preceded by an upper respiratory or gastrointestinal viral disease. Outbreaks of acute flaccid myelitis usually occur in late summer or early fall biannually. Outbreaks of acute flaccid myelitis often coincide with outbreaks of enterovirus-A71 or enterovirus-D68 infection. In addition to the United States, outbreaks of acute flaccid myelitis have been reported in many European and Asian countries. Characteristically, neuroimaging demonstrates abnormalities in the central spinal cord region, affecting the gray matter. Cerebrospinal fluid examination demonstrates lymphocytic pleocytosis. Enterovirus-D68 or -A71 are rarely detected in cerebrospinal fluid examination; however, virus can be identified in other biological specimens like respiratory and fecal specimens. Significant changes in the epidemiology of acute flaccid paralysis during 2019 and 2020 have been noted. Enterovirus D68 was demonstrated in 37 cases in 2018, in one case in 2019, and in none in 2020. Cases reported during 2019 and 2020 were more frequent in older children, and upper limb involvement was less frequent. Preceding febrile or respiratory illness and CSF pleocytosis were also less frequent in late cases. Infectious or parainfectious transverse myelitis, vascular myelopathies, and Guillain-Barré syndrome are important in the differential diagnosis of acute flaccid myelitis. No specific therapy for acute flaccid myelitis is currently available. Acute flaccid myelitis is generally not considered as differential diagnosis among children with acute paralysis, leading to delayed treatment and increased respiratory involvement risk. Immunotherapies like methylprednisolone, intravenous immunoglobulin, or plasmapheresis have no definite role to play. The majority of patients with acute flaccid myelitis require long-term rehabilitation.

Key points

• Acute flaccid myelitis is a polio-like disabling disease, clinically characterized by the acute onset of flaccid limb weakness.

• Acute flaccid myelitis generally affects children and young adults.

• Epidemiological evidence supports an association between enterovirus-D68 and enterovirus-A71 with acute flaccid myelitis.

• MRI of spinal cord demonstrates spinal cord gray matter hyperintensity.

• CSF evaluation shows inflammatory changes with increased lymphocyte count (> 5 cells/mm3) and mild elevation in proteins.

• Treatment with intravenous immunoglobulin, methylprednisolone, or plasmapheresis is generally unsatisfactory.

• Only a few patients recover completely.

• Most of the patients require long-term rehabilitation.

Historical note and terminology

The term “acute flaccid myelitis” was coined in 2014 to describe a cluster of cases with acute flaccid paralysis of undetermined etiology. These cases with polio-like illness were seen in the United States in 2012 (from California) and 2014 (from Colorado). Among five first reported cases of acute flaccid myelitis, two cases had evidence of respiratory tract infection with enterovirus-D68. In 2014, Centers for Disease Control and Prevention (CDC) initiated a surveillance program against acute flaccid myelitis. In 2015, Council of State and Territorial Epidemiologists (CSTE) adopted a standardized case definition for acute flaccid myelitis to categorize all “patient under investigation” either as confirmed or probable cases. In 2020, the case definition was updated further with the purpose of reporting of possible acute flaccid myelitis cases identified postmortem. The latest definition allows to accommodate cases who died and did not have an MRI done but had evidence of myelitis on autopsy (04).

Earlier, in 2005, enterovirus-D68 was implicated in causation of many central nervous system disorders and the virus was identified in the cerebrospinal fluid (19; 25).

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