Objective: The Powassan virus is a rare neurotropic, tick-borne arbovirus associated with meningoencephalitis. Despite the virus’s known predilection for the basal ganglia, there are no reports detailing the spectrum of movement disorders in children with Powassan meningoencephalitis. In this case series, we present three cases of pediatric Powassan encephalitis, highlighting the diverse and evolving movement disorders associated with this disease.

Background: The first reported case dates back to 1958 in a child who presented with fatal encephalitis in the town of Powassan, Ontario, Canada¹. Since then, the number of reported cases in the United States has steadily increased, with cases primarily reported in the country’s Northeastern regions² with a mortality rate of up to 7.1% in the pediatric population³. Powassan virus has an incubation of 1-5 weeks⁴ and a strong tropism for the basal ganglia, thalamus, cerebellum, and brainstem⁵.

Method: Patient/guardian written consent was obtained. This study was approved by the Institutional Review Board at Boston Children’s Hospital (IRB-P00043928).

Results: We observed subcortical myoclonus and progressive generalized dystonia (Patient 1), transient dyskinesias and refractory focal dystonia (Patient 2), and generalized dystonia evolving into chorea and lingual dyskinesias (Patient 3). One patient displayed multifocal vasculitis on MRI angiography, a novel finding. All patients demonstrated bilateral T2 hyperintensities in the basal ganglia on MRI. In the acute period, all patients received high-dose corticosteroids, with two also receiving IVIG, interventions which have been posited to promote clinical improvement.  Two patients required admission for management of worsening dystonia after their acute presentation. All patients required multiple treatments for dystonia and chorea throughout their disease courses, highlighting the refractory nature of their movement disorders.

Conclusion: Movement disorders were a primary source of the morbidity experienced by pediatric Powassan encephalitis patients throughout their disease course, underscoring the importance of regular monitoring and adaptable treatment strategies in this condition. Larger, prospective studies are necessary to fully delineate the spectrum of associated movement disorders in pediatric patients with this rare and severe disease.

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References: 1. McLean DM, Donohue WL. Powassan virus: isolation of virus from a fatal case of encephalitis. Can Med Assoc J. 1959; 80(9): 708–711.
2. CDC. Powassan Virus. 2024. Historic Data (2004-2022). Available from: https://www.cdc.gov/powassan/data-maps/historic-data.html
3. Kakoullis L, Vaz VR, Kaur D, et al. Powassan Virus Infections: A Systematic Review of Published Cases. Trop Med Infect Dis. 2023; 8(12): 508.
4. Doughty CT, Yawetz S, Lyons J. Emerging Causes of Arbovirus Encephalitis in North America: Powassan, Chikungunya, and Zika Viruses. Curr Neurol Neurosci Rep. 2017; 17(2): 12.
5. Finelli PF. MR Imaging Patterns and Prognosis in Powassan Virus Encephalitis. Neurologist. 2024; 29(2): 103–105.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spectrum-and-evolution-of-movement-disorder-phenomenology-in-a-pediatric-powassan-encephalitis-case-series/