2026 American Academy of Neurology Abstract Website

Objective:

To determine characteristic neurological clinicoradiographic presentations of Powassan Virus (POWV) infection.

Background:

POWV is a tick-borne flavivirus endemic to the midwestern and northeastern United States, south-central Canada, and parts of Russia. It is transmitted by commonly encountered Ixodes ticks within as little as 15 minutes of attachment, can cause severe neuroinvasive disease, and infection incidence is increasing. Clinical recognition and diagnosis remain suboptimal partially due to limited knowledge of the spectrum of neurological clinicoradiographic manifestations.

Design/Methods:

We performed a systematic review of neuroinvasive POWV human cases published 1959-2020. “Powassan”, “Powassan Virus”, and “Deer Tick Virus” were searched in PubMed, MEDLINE, Google Scholar, and Scopus. Articles meeting the following criteria were included: published in English; age, gender, and neurological clinical syndrome described; diagnostic method of POWV infection consistent with CDC criteria for probable or confirmed arboviral disease. Articles describing pooled patient populations without details of individual cases and duplicate articles were excluded.

Results:

Initial search yielded 4456 articles. 56 articles with 89 unique cases were included. Median age was 60 years, 67% male. Onset was described in all months except January-March, peaking in July. Geographic distribution was restricted to upper midwestern and northeastern United States and eastern Canada. Meningeal signs/symptoms (67%) and decreased level of consciousness (53%) were common. Seizures occurred in 22%, more commonly in children. Cerebellar signs (31%), eye movement palsies (20%), and lower motor neuron weakness syndromes (13%) were distinctive. In the 40 cases with MRI, basal ganglia (45%), thalamus (38%), cerebellum (35%), brainstem (33%), and hemispheric white matter (18%) were most commonly affected. In-hospital mortality was 15%. Discharge median modified Rankin score was 4 (IQR 1-6).

Conclusions:

Clincicoradiographic manifestations of neuroinvasive POWV preferentially involve the deep gray nuclei, cerebellum, and brainstem. Lower motor neuron weakness syndromes and hemispheric white matter involvement on MRI were unexpectedly frequent. Short-term outcomes were commonly poor.