Abstract
A 72-year-old man presented with a 3-day history of positional rotational vertigo that progressed to continuous vertigo with one episode of vomiting, mimicking acute vestibular syndrome (AVS). Bedside examination revealed spontaneous right-beating horizontal nystagmus and findings consistent with a peripheral pattern on the head impulse, nystagmus, test of skew (HINTS) examination: a positive head impulse test (HIT), unidirectional nystagmus, and no skew deviation. Head shaking with the head flexed forward by 30° reversed the nystagmus to left-beating, and the HIT became positive on rightward impulses. The head yaw test subsequently elicited apogeotropic horizontal positional nystagmus, which converted to a geotropic pattern after repeated head yaw testing and head shaking. Following the Gufoni maneuver, nystagmus and vertigo resolved within one hour. This case demonstrates reversible right horizontal semicircular canal (HSC) canalith jam, a rare benign paroxysmal positional vertigo (BPPV) variant caused by otoconial obstruction of endolymph flow, producing persistent nystagmus and fluctuating sequential labyrinthine hypofunction. Head-shaking maneuver induced a previously unreported bidirectional switch between sustained excitatory and inhibitory cupular deflections within the same canal. Simple bedside maneuvers enabled rapid diagnosis and cure without imaging or drugs. Clinicians should consider HSC canalith jam in AVS with peripheral HINTS when history suggests BPPV.