Unusual cause at an unusual time-Powassan virus rhombencephalitis.

Powassan virus lineage II (POWV) is an emerging tick-borne neurotropic pathogen, transmitted to humans by the bite of infected Ixodes scapularis ticks. In the United States, the disease is most prevalent in the Northeast and the upper Midwest and occurs mostly during the spring and summer months when tick activity is the highest. Some patients infected with POWV develop severe encephalitis, with high mortality. We report the case of a 42-year-old healthy man who developed progressive diplopia and dysarthria in December following a deer hunting trip. Routine blood work was unrevealing and MRI was normal. Extensive work-up for infectious, autoimmune, and paraneoplastic causes was positive only for POWV. The patient was treated with supportive care and intravenous corticosteroids, with an excellent outcome. We present a rare clinical presentation of a potentially fatal emerging disease that responded favorably to corticosteroids.