Acute flaccid myelitis

Last revised by Daniel J Bell on 13 Jun 2022

Acute flaccid myelitis is an uncommon cause of acute flaccid paralysis similar to poliomyelitis, primarily affecting children and usually seen following a respiratory viral illness.  

Acute flaccid myelitis primarily affects children. Cases appear to be temporally related to respiratory enteroviral illness (especially enteroviruses D68 and A71) 1,2. Other implicated viruses include flaviviruses (e.g. West Nile encephalitis and Japanese encephalitis), adenoviruses and herpesviruses 1

Affected individuals typically have a respiratory viral prodrome typically 1 to 4 weeks prior to the acute neurological phase characterized by rapid onset of lower motor neuron pattern weakness in one or more limbs 1,2. Weakness may also involve respiratory muscles 2.   

MRI of the spinal cord demonstrates increased longitudinally extensive spinal cord lesions with T2 signal in the grey matter, particularly the anterior horns 1. The brainstem is involved in up to 35-75% of cases 1,2. A minority of patients may also demonstrate deep cranial grey matter T2 high signal lesion 2

Treatment is primarily supportive with no active treatment being shown to definitely improve long-term outcomes 1,2. Many patients require respiratory support and intubation 2.  

The prognosis is guarded with only 5% of affected individuals reporting complete recovery. The remainder have variable persistent impairment ranging from mild symptoms not affecting function to severe incapacitation requiring complete reliance on carers 1,2

The differential diagnosis is that of acute flaccid paralysis.

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