Acute flaccid myelitis: cause, diagnosis, and management

Abstract

Acute flaccid myelitis (AFM) is a disabling, polio-like illness mainly affecting children. Outbreaks of AFM have occurred across multiple global regions since 2012, and the disease appears to be caused by non-polio enterovirus infection, posing a major public health challenge. The clinical presentation of flaccid and often profound muscle weakness (which can invoke respiratory failure and other critical complications) can mimic several other acute neurological illnesses. There is no single sensitive and specific test for AFM, and the diagnosis relies on identification of several important clinical, neuroimaging, and cerebrospinal fluid characteristics. Following the acute phase of AFM, patients typically have substantial residual disability and unique long-term rehabilitation needs. In this Review we describe the epidemiology, clinical features, course, and outcomes of AFM to help to guide diagnosis, management, and rehabilitation. Future research directions include further studies evaluating host and pathogen factors, including investigations into genetic, viral, and immunological features of affected patients, host-virus interactions, and investigations of targeted therapeutic approaches to improve the long-term outcomes in this population.

Figure 1:. Typical MRI findings in the acute phase of AFM

Spinal MRIs are shown of an 8-year-old child with AFM, acquired 24 h after onset of neurological symptoms.(A) Sagittal T2 image showing an ill-defined longitudinally extensive central/anterior spinal cord lesion. (B) Axial T2 image from C5–C6 shows hyperintensity of the entire grey matter of the spinal cord, with associated oedema and some surrounding white matter hyperintensity. (C) Axial T2 image from T7 shows asymmetric hyperintensity of the grey matter (right more than left). (D) Axial T2 image from T10 shows hyperintensity of the entire grey matter. (E) Axial FLAIR image at the level of the middle cerebellar peduncle demonstrates hyperintensity of the dorsal pons (arrow). AFM=acute flaccid myelitis.

Figure 2:. Diagnostic criteria for AFM

These criteria apply to the acute stage of the disease. AFM=acute flaccid myelitis. H=history. E=examination. CSF=cerebrospinal fluid. P=diagnostic element is present. A=diagnostic item is absent. P/A=presence of this diagnostic element is supportive but not required. ND=test was not done. ADEM=acute disseminated encephalomyelitis. MOG=myelin oligodendrocyte glycoprotein. *Subjective (H1) or objective (E1) weakness must be present in any of: limb(s), neck, or cranial nerves. †Prodromal illness can include respiratory, gastrointestinal, or other symptoms of viral illness. ‡Normal or increased reflexes can be found in other limbs. §If MRI obtained very early (within hours of neurological onset) appears normal, repeat MRI after clinical evolution might show diagnostic findings. MRI obtained at late stages (≥4 weeks) might be normal. ¶CSF may be normal at very early (hours) or late (≥4 weeks) stages of AFM. ||At present, there are no data describing the frequency of these features in patients with AFM.