Novel Case of Bilateral Posterior Semicircular Canal Benign Paroxysmal Positional Vertigo with Asymmetric Mechanisms: Left Cupulolithiasis and Right Short-Arm Canalolithiasis.

Introduction: Benign paroxysmal positional vertigo (BPPV) involving multiple semicircular canals (MC-BPPV) is an uncommon variant in which otoconia dislodged from the utricular macula migrate into two or more canals, provoking brief vertigo episodes with positional changes. The single-canal variant predominates, most often affecting the posterior canal, followed by the horizontal and anterior canals. MC-BPPV typically presents with ipsilateral or contralateral posterior-horizontal canal combinations, while atypical posterior canal variants are rarer and require careful nystagmus evaluation during positional testing. Case Report: A 62-year-old man presented with a one-day history of vertigo triggered by rising from the supine position, along with retropulsion and vertigo during transitions to lateral recumbent positions. Standard right Dix-Hallpike test (DHT) and right half DHT were unremarkable. Augmented right half-DHT elicited persistent upbeat right-torsional nystagmus; a negative inversion test indicated right short-arm posterior canalolithiasis. Left half-DHT evoked persistent left torsional upbeating nystagmus that reversed to downbeating nystagmus with a subtle right-torsional component on right lateral rolling nose-down, consistent with left posterior cupulolithiasis. The Bascule maneuver was used to treat the left ear, and the prone pitch-and-yaw maneuver was used to treat the right ear. Follow-up showed conversion of left posterior cupulolithiasis to typical canalolithiasis, which resolved with the Epley maneuver, resulting in complete symptom remission. Conclusions: This case highlights the importance of comprehensive positional testing and mechanism-specific therapeutic maneuvers for successful management of atypical bilateral MC-BPPV.