Introduction: Enterovirus 71(EV71) causes epidemic disease associated with a wide spectrum of neurological disorders. While poliomyelitis has been almost eradicated, EV71 remains a leading cause of acute flaccid paralysis. The present study examined characteristics of EV71 lower motor neuron(LMN) disease to gain further insight into pathogenesis and natural history.

Methods: Clinical and neuroimaging characteristics together with outcomes were examined in 14 children(age range 0.5-7.8 years, mean 2.1±0.5 years) with proven EV71 infection and acute flaccid paralysis or motor cranial nerve palsy from two epidemics in 2000 and 2013.

Results: Extent of clinical disease was greater in the earlier epidemic(2000-6/6 patients had bilateral multisegment LMN disease involving brainstem motor nuclei, cervical, thoracic and lumbar segments;2013-7/8 patients had focal unilateral paresis-3 upper limb, 3 lower limb, 1 cranial nerve,P=0.005). Neuroimaging differed between epidemics(2000-MRI demonstrated T2-hyperintense lesions in spinal cord/brainstem motor nuclei in 6 patients;2013-no signal changes demonstrated in motor nuclei,P=0.001). 6/6 patients from 2000 had long-term residual weakness and 3/6(50%) required long term ventilation. While the natural history of recent patients is emerging, 3/8 recovered fully (median follow-up 6 months) and no patient remains ventilated.

Conclusion: Focal EV71 disease of LMNs occurs throughout the brainstem and spinal cord, and like polio, often results in permanent paralysis. Outcome may be related to extent of initial disease, neuroimaging involvement of motor nuclei/anterior horn cells and specific epidemic. Differences between epidemics in clinical, neuroimaging and natural history of EV71 LMN disease may relate to subtype and virulence.