A patient displays upbeating and right torsional nystagmus during a right-sided Dix-Hallpike test. Which semicircular canal is most likely affected?

• A. Left posterior canal
• B. Right posterior canal
• C. Left horizontal canal
• D. Right horizontal canal

Answer: (B)

The Dix-Hallpike maneuver that’s performed on the right primarily stimulates the right posterior semicircular canal. When this canal is affected by BPPV, the provocative nystagmus is typically upbeating with a torsional component toward the side being tested. So seeing upbeating vertical nystagmus with a rightward (toward the tested ear) torsional tilt points to a right posterior canal problem.

If the left posterior canal were involved, the torsional component would be toward the left ear. Horizontal canal involvement usually produces predominantly horizontal nystagmus rather than vertical upbeating, which is why those options don’t fit the observed pattern.