A 45-year-old woman with dizziness and nausea; three beats of vertical nystagmus are observed with extraocular movements. Which finding is most likely to indicate the need for immediate transfer to the emergency department?

• A. Dysarthria
• B. Diplopia
• C. Nystagmus on extraocular movements
• D. Normal gait

Answer: (C)

Vertical nystagmus seen during extraocular movements is a red flag for a central origin of dizziness, such as brainstem or cerebellar involvement. In contrast to peripheral vertigo, which usually produces horizontal or rotary nystagmus that can fatigue and tends to spare other neurologic signs, vertical nystagmus suggests a central process that can be life-threatening and requires urgent evaluation and imaging. Therefore, the finding of nystagmus on how the eyes move points most strongly to the need for immediate transfer to the emergency department. Dysarthria or diplopia are concerning as well, but the vertical nystagmus itself is the clearest indicator of a potential central emergency in this scenario, and a normal gait would not indicate the same level of urgent risk.