In the UK, a clinical case of acute flaccid paralysis (AFP) has been defined as an individual of any age presenting with acute onset of flaccid paralysis
affecting one or more limbs, not explained by a non-infectious cause with onset date since 1 January 2018 (1).
- in AFP, in addition to bulbar palsy, the spinal cord, peripheral nerves, neuromuscular junctions, and muscles can all be affected, resulting in sustained functional disability of the extremities (2)
- although enterovirus A71 (EV-A71) is known to cause AFP and other neurological diseases, the exact causes of AFM are still unclear (1,2)
A probable case of acute flaccid myelitis (AFM) was defined as any person with symptoms of AFP and a cerebrospinal fluid (CSF) pleocytosis (white cell count (WCC) > 5 cells/mm^3) (1).
- a confirmed AFM case was defined as any person with symptoms of AFP and a spinal cord lesion largely restricted to grey matter on magnetic resonance imaging (MRI) scanning
- cases typically present clinically as poliomyelitis-like paralysis, affecting one or more limbs, with no apparent sensory loss and characteristic grey
matter findings on MRI - AFM is a subset of AFP that is also characterized by a limb paralytic condition, but it has certain distinct features such as lesions in magnetic resonance imaging of the spinal cord gray matter. AFM leads to spinal cord, brainstem, or motor neuron dysfunction
- clinical phenotypes, pathology, and patient presentation of AFM closely mimic AFP (2)
- AFM is a potentially fatal acute onset of flaccid weakness and muscle immobility in children at a median age of 1 to 7 years
- 90% of cases of AFM are preceded by clinical complications such as febrile and respiratory illness lasting for days or weeks, followed by several symptoms including severe weakness of limb muscles, ptosis, diplopia, dysphagia, or dyspnea, or even respiratory failure
- most AFM patients present with the sudden and rapid onset of muscle fatigue in conjunction with the loss of coordination and balance
- paralysis frequently occurs asymmetrically, and may involve any combination of limbs, with quadriparesis occurring in about 1/3 of cases
- pattern of weakness is consistent with a lower motor neuron process and includes hyporeflexia or areflexia and hypotonia, and (eventually) rapid atrophy of affected limb muscles due to damage to the anterior horn of the spinal cord
- cranial nerve, bowel, and bladder dysfunction might be present
- sensory symptoms may occur but are uncommon
- increase in AFM reports was temporally associated with increased circulation of enterovirus (EV-D68) EV-D68, a common EV infection that seems to circulate biennially in late summer and autumn, which was linked with severe acute respiratory and neurological illness in 2014 and 2016 in Europe, Asia and North America (1)
- it has been noted that there is "considerable debate whether EV-D68, which is recognised to be an almost ubiquitous infection in children, causes AFP/AFM. Although the virus is rarely detected in the CSF, it is frequently found in adequate samples from the respiratory tract"
- prognosis
- most children affected by AFM experience short-term neurological deficits, with significant muscle atrophy in the affected limbs for a year or more following the disease onset
- long-term prognosis for AFM is not yet known, but affected patients can continue to improve slowly over time with ongoing rehabilitation (2)
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