Persistent spontaneous nystagmus following a canalith repositioning procedure in horizontal semicircular canal benign paroxysmal positional vertigo.

IMPORTANCE: Nystagmus can occur spontaneously from multiple causes. Direction-changing positional nystagmus on the supine roll test is a characteristic clinical feature in horizontal semicircular canal benign paroxysmal positional vertigo. One of several mechanisms of spontaneous nystagmus is plugging of the otoconia, which has been described as a canalith jam. OBSERVATIONS: We evaluated a 52-year-old woman with a history of geotropic variant of horizontal semicircular canal benign paroxysmal positional vertigo on the right side who had been treated with a modified Lempert maneuver 3 months earlier. The patient had persistent spontaneous nystagmus, despite a positional change after the canalith repositioning procedure. A bithermal caloric test result demonstrated unilateral canal paresis on the right side. The following day, the patient's symptoms and nystagmus had subsided. On a repeated bithermal caloric test, a normal response was demonstrated on both sides. CONCLUSIONS AND RELEVANCE: To our knowledge, this is the first report of a case that shows on video persistent nystagmus findings consistent with a canalith jam. We discuss a possible mechanism underlying this phenomenon.