いわゆる Heavy cupula 症例および Light cupula 症例の患側と眼振の特徴

抄録

　Lesion side and mean slow phase velocity of horizontal positional nystagmus (SPVH) were investigated in 35 patients with heavy cupula (HeC), consisting of 17 cases of lateral canal benign paroxysmal positional vertigo (BPPV)-canalolithiasis apogeotropic type (L-ca-apo) and 18 cases of L-BPPV―cupulolithiasis (L-cu), and 18 patients with light cupula (LiC). The Neutral position (NP), where the direction of horizontal nystagmus reverses, existed on the right-or left-ear-down head position in the supine position and was near the upright sitting position in the sagittal plane in the patients with HeC and LiC. In the HeC patients, the SPVH was significantly greater in the non-NP down position (n-NDP), compared with the NP down position (NDP), and was significantly greater in the supine position (SP) than in the prone position (PP). The ratio of SPVH in the n-NDP to the SP and the ratio of SPVH in the PP to the SP in the patients with L-ca-apo were significantly greater and lower than those in the patients with L-cu, respectively. In the LiC patients, the SPVH was significantly lower in the SP than the PP but was not significantly different between the n-NDP and the NDP. Taking Ewald's second law into consideration, the ratios of SPVH were not significantly different between the patients with LiC and the patients with L-cu. In HeC or LiC, when the direction of horizontal nystagmus in the SP reverses relative to that in the PP, the side of the NP when the patient is in a supine position indicates the lesion side. Asymmetrical responses in the head roll test do not always indicate the lesion side in patients with HeC and do not indicate the lesion side in patients with LiC. The weight of the affected cupula, the angle of the head rotation, the angle of the NP and Ewald's second law seem to determine the direction of the nystagmus and the SPVH. The ratios of the SPVH in the SP and the SPVH in the PP seem to be determined by Ewald's second law. The different SPVH ratios between the L-ca-apo and L-cu groups can probably be explained by the fact that the otoconia mass is in partial contact with the cupula in the patients with L-ca-apo, whereas the mass is in full contact with the cupula in the patients with L-cu. These differences in pathophysiology between LiC and L-cu patients seem to be responsible for the weight change of the cupula.