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Powassan virus (POWV) is a rare flavivirus prevalent in the New England region. It can cause meningoencephalitis, with a case-fatality-rate of 10-15%. Nearly 50% of those with neurological involvement develop long-term sequelae, ranging from headaches to paralysis. We present a case of an elderly female with Powassan encephalitis. Although cases have risen in the United States over the past decade, less than 300 cases have been reported since its discovery in 1958.

A 77-year-old woman presented to the emergency department with acute-onset left leg weakness. She was admitted for stroke workup. She endorsed multiple tick bites three weeks prior. In the next two days, she developed quadriplegia and febrile encephalopathy. Broad-spectrum antibiotics were initiated due to concerns for meningitis, and she was intubated and transferred to our Neuro-ICU. A contrasted-MRI showed symmetric T2 FLAIR hyperintensities in the basal ganglia, thalami, frontal lobes and cerebellum with subtle contrast enhancement. CSF analysis revealed 76 cells/cubic mm (lymphocytes) and 130mg/dL protein. Extensive panels for bacterial, viral, and arboviral etiologies were negative. Ultimately, Powassan IgM antibody and PCR in the CSF resulted positive.  She underwent tracheostomy and PEG placement and had unfortunately made no improvement by week 6. Subsequently, her family elected for comfort measures, and she was compassionately extubated.

This case alerts us to consider POWV with relevant clinical and radiological findings, especially in an endemic area. A systematic review of 84 POWV cases in North-America and Canada showed paralysis in 44.1% of patients and cognitive deficits in 33.3%. 

POWV encephalitis is underrecognized. Confirmatory testing can provide a diagnosis, but treatment remains largely supportive. Our research showed that high dose steroids don’t improve outcomes, and available IVIG lacks antibodies against POWV. Younger patients, with milder symptoms of encephalitis, can recover with minimal deficits-vouching for aggressive ICU care.