A 58-year-old man reports brief episodes of rotatory vertigo when rolling over in bed to either side. The supine head roll (Pagnini-McClure) test reveals horizontal nystagmus that beats toward the lowermost ear on both sides, with latency and fatigability. The most likely diagnosis is:

• A Posterior semicircular canal BPPV due to cupulolithiasis
• B Lateral (horizontal) semicircular canal BPPV due to canalithiasis ✓
• C Anterior semicircular canal BPPV due to canalithiasis
• D Central positional vertigo from a cerebellar lesion

Explanation

Geotropic (toward the ground, i.e., toward the undermost ear) horizontal nystagmus on the supine roll test indicates free-floating otoconia in the non-ampullary arm of the lateral canal, which settle ampullopetally in the dependent canal and excite it: canalithiasis of the undermost canal. Latency and fatigability confirm a peripheral origin. Apogeotropic nystagmus instead suggests cupulolithiasis, where debris adheres to the cupula and makes it gravity sensitive.

Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.