A 47-year-old woman reports vertigo whenever she rolls over in bed. Testing shows nystagmus that begins immediately on assumption of the provocative position, is purely downbeating without torsion, persists beyond two minutes, and does not fatigue on repeat positioning. Neuroimaging would be most likely to reveal:

• A A lesion of the cerebellum or cervicomedullary junction ✓
• B Canalithiasis of the posterior semicircular canal
• C Endolymphatic hydrops of the affected labyrinth
• D Superior semicircular canal dehiscence overlying the tegmen tympani

Explanation

Central positional nystagmus begins without latency, outlasts one minute, does not fatigue, and may be purely vertical or direction-changing, reflecting cerebellar or brainstem involvement such as a tumour, Chiari malformation, or degenerative disease. Anterior canal BPPV can also be downbeating, but its short latency, brief duration, and fatigability distinguish it, which is exactly why those features were specified in the stem.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.