Which statement best describes posterior canal benign paroxysmal positional vertigo (BPPV) in diagnostic testing?

• A. Nystagmus is purely horizontal with Dix-Hallpike
• B. Dix-Hallpike elicits no vertigo in posterior canal BPPV
• C. A torsional upbeating nystagmus is observed during Dix-Hallpike indicating posterior canal involvement
• D. Dix-Hallpike tests the inferior canal (not posterior)

Answer: (C)

The key idea is that posterior canal BPPV produces a distinctive eye movement pattern during the Dix-Hallpike maneuver. When otoconia are in the posterior canal, moving the head into the Dix-Hallpike position causes gravity to move those particles within the canal, stimulating the hair cells in a way that generates a quick, combined torsional and vertical (upbeat) nystagmus. The torsional component is tied to the orientation of the posterior canal, and the vertical component is upwards, with the fast phase typically directed toward the upper eye poles. This specific pattern—torsional upbeating nystagmus observed during Dix-Hallpike—is the best indicator that the posterior canal is involved, and it also aligns with the patient’s brief vertigo during the maneuver.

The other statements don’t fit because pure horizontal nystagmus is more characteristic of horizontal canal BPPV; Dix-Hallpike reliably elicits vertigo in BPPV, not its absence; and Dix-Hallpike is designed to test the posterior canal rather than the so-called inferior canal, which is not the target of this maneuver.