SHM Converge Scientific Abstract ePoster Gallery-Tick Bite, Rash, and a Red Herring: Powassan Encephalitis in Disguise

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A 47-year-old woman with rheumatoid arthritis on methotrexate developed diplopia, dysarthria, gait instability, weakness, headache, fever, and meningoencephalitis after a tick bite in Minnesota with a targetoid rash. She was initially diagnosed clinically with Lyme disease and treated with doxycycline, but her neurologic symptoms worsened, prompting hospital admission and neurocritical care monitoring.<br /><br />Workup showed lymphocytic pleocytosis and elevated CSF protein, with brain MRI abnormalities in the posterior fossa. A broad infectious evaluation was largely negative, including bacterial/viral CSF panel, Lyme serologies, and PCRs for other tick-borne pathogens. Serologies for West Nile and St. Louis encephalitis showed likely cross-reactive IgG positivity without IgM evidence of acute infection. Powassan virus testing was ultimately diagnostic: serum IgM was positive and confirmatory plaque reduction neutralization testing returned a high titer of 1:5120, confirming Powassan virus encephalitis. CSF PCR was negative, consistent with the limited sensitivity of molecular testing once neuroinvasive symptoms begin.<br /><br />She received doxycycline, ceftriaxone, high-dose IV methylprednisolone, and IVIG, with subjective improvement. She was discharged to acute rehabilitation, later showing marked recovery with minimal residual deficits at follow-up.<br /><br />The case highlights that in immunocompromised patients, clinicians should maintain a broad differential diagnosis for meningoencephalitis, even when the presentation seems to fit Lyme disease. Powassan virus is an emerging, potentially fatal tick-borne arbovirus with overlapping symptoms and shared vectors, making diagnosis challenging. Early recognition, improved access to confirmatory testing, and further study of therapies are important for managing high-risk patients.

Asset Subtitle

Gracen Betts

Meta Tag

Author List Annie Massart, Gracen Betts, Milee Nelson, Myriam Shehata, Sarah Chung

Category Clinical Vignettes

Concept Powassan Virus Encephalitis

Concept Meningoencephalitis

Concept Immunocompromised State

Concept Tick Exposure

Concept Tick-Borne Infection

Distinguished Non-Finalist

Presenter Organization Emory University School of Medicine

Presenting Author Gracen Betts

Track Adult

Keywords

Powassan virus encephalitis

tick-borne meningoencephalitis

rheumatoid arthritis

methotrexate immunosuppression

Lyme disease differential

Minnesota tick bite

diplopia and dysarthria

CSF lymphocytic pleocytosis

posterior fossa MRI abnormalities

IVIG and corticosteroid treatment

Powassan Virus Encephalitis

Meningoencephalitis

Immunocompromised State

Tick Exposure

Tick-Borne Infection