末梢性方向交代性頭位眼振と外側半規管型良性発作性頭位めまい症

抄録

　Direction-changing positional nystagmus caused by a peripheral vestibular lesion (DCPN) can be classified into the geotropic and apogeotropic types, based upon the direction of horizontal nystagmus in the right ear down position and the left ear down position, and also paroxysmal and persistent types based upon the duration of horizontal nystagmus. The incidence of DCPNs was estimated and cases that converted from apogeotropic to geotropic DCPN were reported. During the course of 9 years and 5 months, 230 patients had DCPN. Among these, 90 patients had paroxysmal geotropic DCPN, 90 had persistent apogeotropic DCPN and 50 had persistent geotropic DCPN. In 90 cases with persistent apogeotropic DCPN, 59 cases (66%) converted to paroxysmal geotropic DCPN during the head roll test or after performing the barbecue rotation of 360° towards the healthy side. The pathophysiology was estimated that lateral semicircular canal benign paroxysmal positional vertigo (BPPV) (canalolithiasis, the debris being located in the anterior part of the canal) changed to lateral semicircular canal BPPV (canalolithiasis, the debris being located in the posterior part of the canal). Furthermore, 2 cases of persistent apogeotropic DCPN that converted to persistent geotropic DCPN naturally without physiotherapy were also reported. To compare persistent apogeotropic DCPN and persistent geotropic DCPN in these cases, the directions of nystagmus were completely reversed in the right side down position and in the left side down position, and also reversed in the supine position and in the prone position, changing in the nearly sitting position. It was shown that both types of DCPN were identical with respect to the affected side and pathogenesis, but small differences or changes in the pathophysiology might lead to both types of DCPN. The pathophysiological mechanism(s) underlying persistent apogeotropic DCPN and persistent geotropic DCPN remain unknown.