A patient with horizontal canal BPPV undergoes the supine roll test. On turning the head to the RIGHT, ageotropic nystagmus (beating away from the ground) is observed that is STRONGER on the right side. This pattern indicates:

• A Right horizontal canal canalithiasis
• B Left horizontal canal canalithiasis
• C Right horizontal canal cupulolithiasis ✓
• D Left horizontal canal cupulolithiasis

Explanation

Ageotropic direction-changing nystagmus that is stronger when turning toward the affected side indicates cupulolithiasis. The heavy cupula deflects away from gravity when the affected ear is down, producing ampulopetal inhibition and ageotropic nystagmus. Stronger nystagmus on the right with ageotropic pattern indicates RIGHT horizontal canal cupulolithiasis. Canalithiasis produces geotropic nystagmus.

Reference: Cummings Otolaryngology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.