Enterovirus D68 Acute Flaccid Myelitis

Acute flaccid myelitis is a poliomyelitis like illness with acute flaccid limb weakness, mostly in children, with spinal grey matter lesions. It is linked to enterovirus D68 and A71 in biennial late summer outbreaks, usually after a febrile respiratory illness.

Pathophysiology. The virus infects anterior horn motor neurons and brainstem motor nuclei, and then causes neuronal loss.

Acute asymmetric flaccid weakness of one or more limbs over hours to days, with reduced or absent reflexes, preserved or mildly altered sensation, neck, facial or bulbar weakness, and respiratory failure in some. Pain in the neck or limb is frequent. Bladder dysfunction occurs.

Red flags.

• Falling forced vital capacity or breathing effort.
• Bulbar weakness and aspiration.
• Rapid progression of limb paralysis.

MRI of the spine shows longitudinally extensive T2 hyperintensity of central grey matter, anterior horn, and brainstem lesions. CSF shows mild pleocytosis and raised protein. Test CSF and respiratory samples (nasopharyngeal and stool) by PCR for enteroviruses. Nerve conduction studies show reduced motor amplitudes with normal sensory responses, and electromyography shows denervation after 1 to 2 weeks. Exclude Guillain-Barre syndrome, poliovirus, MOG antibody disease and transverse myelitis.

Differential diagnosis.

• Guillain-Barre syndrome, transverse myelitis and MOG antibody disease.
• Poliomyelitis, West Nile virus and spinal cord infarct.
• Myasthenia gravis and botulism.

No treatment has proved effective. Management is supportive.

Respiratory care. Monitor forced vital capacity and negative inspiratory pressure every 4 to 6 hours, intubate early for bulbar failure or failing respiratory function.

Immune therapy. Controlled evidence is lacking. Intravenous immunoglobulin 2 g/kg over 2 to 5 days or corticosteroids are often used early, but benefit is unproven. Steroids may increase viral replication and are avoided by some.

Rehabilitation. Early physiotherapy and occupational therapy, bracing, and nerve or tendon transfer surgery after 12 months when recovery plateaus (best results are in selected children).

Pain. Gabapentin 5 mg/kg three times daily (adjust for renal function) for neuropathic pain.

Prevention. Hand hygiene and respiratory precautions. Report cases to public health authorities.

Prognosis. Most have persistent motor deficit, with partial recovery over 1 to 2 years.

Monitoring. Respiratory function, swallowing, strength and bladder.

Referral and escalation. Admit, with intensive care for respiratory risk, and refer to paediatric neurology.