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Spontaneous canalith jam is an uncommon form of benign paroxysmal positional vertigo mimicking acute vestibular neuritis. We described for the first time a spontaneous horizontal semicircular canalith jam associated with a typical canalolithiasis involving contralateral posterior semicircular canal (PSC), illustrating how the latter condition modified direction-fixed nystagmus during head movements. An 81-year-old woman with persistent vertigo referred to our center. Video-Frenzel examination showed horizontal direction-fixed right-beating nystagmus in primary gaze position, inhibited by visual fixation. She exhibited corrective saccades after leftward head impulses. Chin-to-chest positioning at the head-pitch test did not modify spontaneous nystagmus, whereas slight torsional components with the top pole of the eye beating toward the right ear appeared in backward head-bending, resulting in mixed horizontal-torsional nystagmus. At supine positioning tests, direction-fixed nystagmus turned into direction-changing geotropic horizontal nystagmus, which was stronger on the left side, while overlapping upbeat nystagmus with torsional right-beating components appeared on the right. Primary clinical findings were consistent with a left horizontal semicircular canalith jam, inducing a persistent utriculofugal cupular displacement, combined with a typical right-sided PSC-canalolithiasis. Once canalith jam crumbled, resulting in a non-ampullary arm canalolithiasis of the horizontal semicircular canal, both involved canals were freed by debris with appropriate repositioning procedures. [ABSTRACT FROM AUTHOR]