In BPPV, cupulolithiasis differs from canalolithiasis in that the displaced otoconia:

• A Float freely within the long arm of the canal, giving fatigable nystagmus with latency
• B Are deposited on the utricular macula, causing constant disequilibrium
• C Occlude the common crus, abolishing all canal responses
• D Adhere to the cupula, rendering it gravity sensitive and producing persistent, non-fatiguing positional nystagmus ✓

Explanation

In cupulolithiasis, otoconial debris becomes adherent to the cupula of the semicircular canal, making it heavier than endolymph and deflection sensitive to gravity. The resulting positional nystagmus begins immediately, persists as long as the provocative position is held, and does not fatigue with repetition. In canalolithiasis, free-floating debris in the canal produces nystagmus after a latent period of a few seconds, which fatigues and habituates. This distinction explains why cupulolithiasis responds less well to simple repositioning manoeuvres.

Reference: Cummings Otolaryngology: Head and Neck Surgery, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.