Abstract Details

Title Clinical and Post-acute Features of Powassan Virus Encephalitis in a High-volume Northeastern Hospital System

Topic Infectious Disease

Presentation(s) S9 - Neuroinfectious Disease: Associations and Outcomes (3:30 PM-3:42 PM)

Poster/Presentation
Number 001

Objective

To describe the clinical presentation, diagnostic features, and outcomes of Powassan virus encephalitis.

Background

Powassan virus is an emerging cause of tick-borne encephalitis with high morbidity and mortality. The clinical spectrum of this disease remains incompletely characterized.

Design/Methods

We performed a retrospective chart review of all adults with positive Powassan virus testing and a compatible neuroinvasive syndrome between 2016 and 2025 in a large, northeastern United States hospital system.

Results

Thirty-eight patients met inclusion criteria. The median age was 67.5 years (range 34–86) and 15 (39%) were female. Presentation to care occurred in all months except February, with a median symptom duration of 4 days. Seventeen patients (45%) had a history of hematologic malignancy or immunosuppression. Encephalopathy was present in 34 (89%), ataxia in 19 (50%), and brain MRI abnormalities in 34 (89%), with cerebellar involvement in 25 (66%). CSF pleocytosis was present in 34/37 (92%), with a median nucleated cell count of 80 (range 1–938). Positive Powassan virus testing included serum IgM in 18 (47%), CSF IgM in 24 (63%), CSF metagenomic next-generation sequencing in 8 (21%), and CSF PCR in 4 (11%). All patients with positive CSF PCR had hypogammaglobulinemia. In-hospital mortality was 21% (8 patients), and 1-year mortality was 32% (12 patients). Nine patients (24%) developed parkinsonism, and 3 (33%) of those improved with levodopa. EMG/NCS performed in 8 patients showed radiculopathies and/or neuropathies in 5 patients.

Conclusions

This study represents the largest known series of Powassan virus encephalitis. The disease is associated with high morbidity and mortality. Encephalopathy and ataxia are common, and cerebellar MRI findings may aid diagnosis. CSF profiles vary. IgM-based testing is standard, PCR-based testing may add value in immunocompromised patients. Post-infectious parkinsonism and peripheral nervous system involvement are underrecognized. Clinicians should consider Powassan virus in patients with encephalitis and exposure to endemic areas.

Authors/Disclosures
George K. Harrold, MD (Brigham and Women's Hospital) PRESENTER	Dr. Harrold has nothing to disclose.
Erik Klontz, MD, PhD	Dr. Klontz has nothing to disclose.
Yutika Singh, Bachelor's in Speech Pathology	Ms. Singh has nothing to disclose.
Isaac H. Solomon, MD, PhD	The institution of Dr. Solomon has received research support from SafeLinkZ, LLC. Dr. Solomon has received publishing royalties from a publication relating to health care.
Jacob E. Lemieux, MD, PhD	The institution of Dr. Lemieux has received research support from National Institutes of Health. The institution of Dr. Lemieux has received research support from Centers for Disease Control and Prevention . The institution of Dr. Lemieux has received research support from Moderna.
Shibani S. Mukerji, MD, PhD (Massachusetts General Hospital)	Dr. Mukerji has received personal compensation in the range of $500-$4,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for Dynamed. Dr. Mukerji has or had stock in Gilead Science.Dr. Mukerji has or had stock in Ranpack.Dr. Mukerji has or had stock in Snowflake. An immediate family member of Dr. Mukerji has or had stock in Amgen. The institution of Dr. Mukerji has received research support from NIH. The institution of Dr. Mukerji has received research support from Massachusetts General Hospital.
John Branda, MD	An immediate family member of Dr. Branda has received personal compensation for serving as an employee of Informed DNA. Dr. Branda has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Tarsus Pharmaceuticals. Dr. Branda has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Flightpath Biosciences. The institution of Dr. Branda has received research support from Analog Devices Inc.. The institution of Dr. Branda has received research support from Pfizer Inc.. Dr. Branda has received publishing royalties from a publication relating to health care. Dr. Branda has received publishing royalties from a publication relating to health care. Dr. Branda has a non-compensated relationship as a Investigator with Karius Inc. that is relevant to AAN interests or activities. Dr. Branda has a non-compensated relationship as a Investigator with Kephera Diagnostics that is relevant to AAN interests or activities.

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