Horizontal semicircular canal jam: Two new cases and possible mechanisms.

Introduction: Benign paroxysmal positional vertigo (BPPV) of the horizontal semicircular canal (hSCC) can present with otoconia blocking its lumen (canalith jam), with signs and symptoms that make it difficult to distinguish from central nervous system pathology. Objective: Here we report two cases of canalith jam affecting the hSCC and offer a theoretical mechanism based on known vestibular neurophysiology. Methods: We use video‐oculography to document the canalith jam and show the moment the otoconia loosen. Results: Canalith jam is a rare form of BPPV remedied with repositioning maneuvers. Conclusion: Clinicians should consider canalith jam as a mechanism for BPPV when the nystagmus is (a) Direction fixed with fixation removed and during positional testing; (b) Velocity dependent on supine head position; (c) Converts to geotropic directional changing nystagmus. [ABSTRACT FROM AUTHOR]