Headache, Ataxia, and Sixth Nerve Palsy in Connecticut
Clinical Vignette
A 56-year-old woman living in rural Connecticut presents in early summer with 4 days of progressive bifrontal headache, nausea, and new gait instability. On the day of admission, she develops horizontal diplopia.
She reports gardening and hiking frequently. One week prior to symptom onset, she removed a small tick from her posterior thigh after noticing it “briefly attached” following an evening walk. She estimates the tick was attached for less than 6 hours. She discarded the tick. She has no rash. She has not traveled outside New England. Past history is notable only for well-controlled hypertension.
On examination she is afebrile and alert. Neurologic exam reveals truncal ataxia and a left abducens (VI) nerve palsy. Strength is full in all extremities.
MRI brain with and without contrast shows patchy T2/FLAIR hyperintensity involving the thalami and dorsal brainstem without a focal abscess. Lumbar puncture reveals 160 WBC/mm³ with a lymphocytic predominance (80%), protein 85 mg/dL, and glucose 60 mg/dL (serum glucose 95 mg/dL). CSF Gram stain and bacterial culture are negative.
CSF meningitis/encephalitis PCR panel is negative (including HSV-1/2, VZV, enterovirus, HHV-6). Serum and CSF testing for Lyme disease is sent. Given the geography and neuroinvasive presentation further testing is also pursued.
Question
What is the most likely diagnosis?
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Question 2
Which statement best distinguishes Powassan virus risk from other deer tick–transmitted infections?
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References
Feder HM Jr, Telford SR III, Goethert HK, Wormser GP. Powassan Virus Encephalitis Following Brief Attachment of Connecticut Deer Ticks. Clinical Infectious Diseases. 2020;73(7):e2350–e2354.