We describe a rare case of spontaneous upbeat nystagmus (UBN) attributable to a canalith jam involving the anterior semicircular canal (ASC) in a patient in whom comprehensive vestibular assessment was useful to identify the underlying pathomechanism. A 56-year-old woman with unsteadiness following repositioning procedures for left-sided benign paroxysmal positional vertigo (BPPV) presented with spontaneous UBN that showed slight right torsional components. A vestibular test battery detected isolated left ASC hypofunction on a video-head impulse test (Video-HIT). We postulated a persistent utriculopetal deflection of the left ASC cupula, which was attributable to entrapment of debris in a narrow canal tract, with consequent sustained inhibition of the ampullary afferents. Although spontaneous UBN receded after impulsive physical therapy, unsteadiness deteriorated into positional vertigo secondary to canalolithiasis involving the ipsilateral posterior canal. In our view, physical therapy possibly fragmented the canalith jam and released free-floating otoconia that eventually settled into the ipsilateral posterior canal. Video HIT revealed normalization of ASC hypofunction, and leftsided posterior canal canalolithiasis was successfully treated using appropriate repositioning procedures. We propose that a canalith jam involving the ASC should be considered in the differential diagnosis of spontaneous UBN, particularly in patients with a history of BPPV and isolated ASC hypofunction detected on video HIT.

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.