仰臥位と腹臥位で眼振方向が変化した一例

抄録

　Direction-changing positional nystagmus is commonly observed in patients with benign paroxysmal positional vertigo of the horizontal semicircular canal type. There are two types, namely, attenuating geotropic nystagmus and persistent apogeotropic nystagmus. The former is thought to be caused by canalolithiasis with the debris located in the horizontal semicircular canal and the latter is caused by cupulolithiasis with the heavy debris attached to the cupula of horizontal semicircular canal. In addition, there are rare cases of persistent direction-changing positional nystagmus, in which the nystagmus does not decay and is of long duration. The pathogenesis of this type of nystagmus is thought to involve a light cupula, because it is explained by the deflection of the cupula in the antigravity direction, but the precise mechanism is still unknown. We encountered a case of vestibular Meniere's disease with recurrent attacks of vertigo, in which the direction of nystagmus changed between the supine and prone positions, and stopped at about 90 degrees below the left and right ears.