What is the Dix-Hallpike test used to diagnose, and which canal does it predominantly assess?

• A. Lateral canal BPPV; tests canalithiasis
• B. Posterior canal BPPV; tests for canalithiasis/cupulolithiasis of the posterior canal
• C. Anterior canal BPPV; tests cupulolithiasis
• D. Superior canal dehiscence; assesses reflex gaze

Answer: (B)

Dix-Hallpike is used to diagnose benign paroxysmal positional vertigo that arises from debris in the posterior semicircular canal. The maneuver positions the head and body so that gravity efficiently stimulates the posterior canal, making vertigo and a characteristic nystagmus more likely if that canal is affected. The typical eye movement is an upbeat nystagmus with a torsional component toward the downward ear, reflecting involvement of the posterior canal. This test can reveal either canalithiasis (free-floating crystals in the canal) or cupulolithiasis (crystals attached to the cupula), since both produce positional vertigo and canal-specific nystagmus patterns, though their timing and persistence can help differentiate them clinically.

The other options don’t fit as well: lateral canal BPPV is best assessed with maneuvers that specifically roll the head and provoke symptoms in the horizontal canal; anterior canal BPPV is much less common and produces different (often downbeat) nystagmus patterns; and superior canal dehiscence is a different disorder altogether, typically evaluated with tests focusing on sound- or pressure-induced vertigo and gaze-related reflexes, not the Dix-Hallpike.