Acute flaccid myelitis: cause, diagnosis, and management

Summary

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.

Introduction

Unusual clusters of a disabling, polio-like illness, now termed acute flaccid myelitis (AFM), were recognised in California in 2012, and Colorado in 2014.1, 2 AFM is now recognised as a global disease, with hundreds of cases reported across Europe,3, 4 Asia,5, 6, 7 Australia,⁸ Africa,⁹ North America,10, 11 and South America.12, 13 Epidemic enteroviral infection is believed to be the main driver of AFM in recent years, particularly enterovirus D68 infection.¹⁴ Cases have usually occurred in geographical clusters, with a distinct seasonal biennial pattern in temperate regions.¹⁵ AFM most frequently affects young children, and is characterised by acute onset of flaccid weakness of one or more limbs, with MRI showing abnormalities of the spinal cord grey matter.⁵ Trunk, neck, respiratory, bulbar, facial, and extraocular muscles can also be affected. The clinical presentation of AFM may mimic other causes of acute weakness such as Guillain-Barré syndrome, demyelinating myelitis, and other infectious myelitis. The diagnosis of AFM can be informed by interpretation of the clinical features alongside findings of laboratory, neuroimaging, and electrophysiological tests.

Acute management of AFM is largely supportive because there is an absence of therapeutic agents proven to alter outcomes. A substantial proportion of patients with AFM will become critically ill during the acute illness, requiring intubation due to respiratory failure or severe bulbar weakness.16, 17 Neurological recovery after AFM is usually incomplete, with many patients having substantial residual weakness and muscle atrophy. Over the long term, patients can be affected by a range of neurological, musculoskeletal, and psychological sequelae.18, 19, 20 Appropriate rehabilitation can improve functional status and quality of life after AFM.¹⁹ Additionally, surgical approaches including tendon or nerve transfer surgery have been used in individual cases to manage residual impairments.21, 22 In this Review we describe the epidemiology, clinical features, course, and outcomes of AFM to help to guide diagnosis, management, and rehabilitation.