Benign paroxysmal positional vertigo (BPPV) is a common cause of episodic vertigo in which otoconia become detached from the macula of otolith organs and either flow freely in the semicircular canals or become attached to the cupula. BPPV of the lateral canal (lcBPPV) is less commonly diagnosed than posterior canal BPPV (pcBPPV), with the supine roll test and Dix-Hallpike test being the primary diagnostic tests, respectively. BPPV is usually treated with particle repositioning maneuvers: the Epley or Semont maneuvers for pcBPPV and the Gufoni, Zuma, or Lempert (barbeque roll) maneuvers for lcBPPV. 

A 19-year-old woman came to the emergency department with acute vertigo and unsteadiness triggered by changing head position. Before emergency department physicians saw her, she was enrolled in a clinical trial where her eye movements were examined with video-oculography. She was then separately assessed by emergency department physicians. Based on bedside evaluation, she was diagnosed with a left-sided BPPV, presumably pcBPPV, and treated with a left-sided Epley maneuver. Her symptoms and nystagmus were documented as resolved by the emergency department physicians, and she was discharged. However, upon analysis of the initial video-oculography testing results, the pattern of her nystagmus was most consistent with right-sided lcBPPV. Thus, the incorrect side and incorrect canal were diagnosed clinically, and the incorrect treatment was applied (Epley for pcBPPV instead of specific maneuvers for lcBPPV). To explain her successful outcome, we simulated the movement of otoconia within the labyrinth in a right-sided lcBPPV in response to correctly and incorrectly performed Epley maneuvers for a left-sided pcBPPV. 

This case and our simulations emphasize that maneuvers designed to induce the movement of displaced otoconia in one specific canal can trigger or treat BPPV in other canals. We recommend that clinicians follow standardized testing protocols to ensure correct diagnosis and treatment of BPPV.