Continuous vertigo and spontaneous nystagmus due to canalolithiasis of thehorizontal canal

The authors present a patient with benign paroxysmal positional vertigo of the right horizontal semicircular canal who developed persistent vertigo wi th spontaneous horizontal nystagmus to the left and caloric hypoexcitabilit y on the right after a head shaking maneuver. Both spontaneous nystagmus an d canal paresis resolved after repeated shaking of the head. The most proba ble mechanism of this type of vertigo is plugging of the horizontal canal b y otoconial particles with a negative endolymph pressure between plug and c upula.