Benign paroxysmal positional vertigo (BPPV) is a common cause of episodic vertigo in which otoconia (calcium carbonate crystals) become detached from their normal location on the macula of the otolith organs.[1] They can then find their way into the semicircular canals (SCC), become free-floating or attached to the cupula, and create abnormal sensations of motion when the position of the head is changed with respect to the pull of gravity. BPPV of the horizontal canal (hcBPPV) is less commonly diagnosed than BPPV of the posterior canal BPPV (pcBPPV), in part because most emergency department and primary care physicians do not attempt to distinguish the canal variants.[2, 3] The supine roll test (SRT) is primarily used to diagnose hcBPPV, while the Dix-Hallpike test is primarily used to diagnose pcBPPV.[4, 5]

BPPV is usually treated with particle repositioning maneuvers that move the otoconia out of the SCC: the Epley or Semont maneuvers for pcBPPV and, for example, the Gufoni, Zuma, or Lempert (barbeque roll) maneuvers for hcBPPV.[4-7] We report here a woman with hcBPPV who came to the emergency department with acute positional vertigo and positional nystagmus and experienced a favorable outcome despite the wrong side and the wrong canal being diagnosed and consequently receiving the wrong treatment maneuver. To explain this seeming paradox, we simulated the movement of otoconia within the labyrinth in a right-sided hcBPPV in response to an Epley treatment maneuver for left-sided pcBPPV. Our simulations suggest that an extended Epley maneuver (i.e., the patient’s head being turned beyond the conventional 45^o angle to 60^o in the second step) caused the otoconia to leave the horizontal SCC, resulting in this patient’s successful outcome.