Using an infrared CCD camera and electronystagmography, we observed positional nystagmus in 36 patients with peripheral positional vertigo. Patients were classified into two categories; (a) the lateral type (n=18): horizontal nystagmus occurs in the lateral position and (b) the sagittal type (n=18): rotatory nystagmus occurs in the headhanging position. In the lateral type, we performed the rolling procedure for 15 patients, and in the sagittal type, we performed the canalith repositioning procedure (CRP). The direction of positional nystagmus reversed in six patients (40%) with the lateral type after the rolling procedure, and 1 patient showed spontaneous change in the direction of positional nystagmus without any procedure. Therefore, we cannot discriminate between peripheral and central origin by the direction of positional nystagmus alone. Soon after CRP, 7 patients (39%) showed the disappearance of positional nystagmus and 3 patients (17%) showed a reverse in the nystagmus direction. In sixteen patients (89%) with the sagittal type, CRP was effective. The free-floating particles theory explains the immediate change of positional nystagmus and the usefulness of CRP. We suggest that lesions in the lateral type involve the lateral semicircular canal, and that in the sagittal type involves the posterior semicircular canal.
