A 55-year-old woman reports brief episodes of rotatory vertigo lasting under a minute when she rolls over in bed or looks upward. Dix-Hallpike testing reproduces vertigo with geotropic torsional nystagmus after a short latency. The most likely mechanism is:

• A Demyelination of the eighth nerve root entry zone
• B Rupture of the round window with perilymph fistula
• C Endolymphatic hydrops distending the membranous labyrinth
• D Free-floating otoconial debris within the posterior semicircular canal ✓

Explanation

The latency, fatigability, brief duration, and positional provocation are classic for benign paroxysmal positional vertigo caused by canalithiasis: detached otoconia from the utricular macula float freely in the posterior semicircular canal and deflect the cupula during position change. Endolymphatic hydrops describes Meniere disease, which produces spontaneous episodes lasting minutes to hours with hearing loss, so it cannot explain a strictly positional, seconds-long nystagmus.

Reference: Ganong Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.