title: Cupulolithiasis of the posterior semicircular canal.
abstract: BACKGROUND
  We sometimes experience patients with persistent torsional/vertical (upbeating) positional nystagmus in the head-hanging position. We have been convinced of the existence of cupulolithiasis of the posterior semicircular canal because such cases reveal persistent torsional/vertical (downbeating) positional nystagmus in the nose-down position.
  
  
  OBJECTIVE
  In order to confirm the validity of Ewald's third law, we quantified the difference between positional nystagmus in the head-hanging position and that in the nose-down position.
  
  
  METHODS
  The subjects were 10 patients with posterior cupulolithiasis, 9 female and 1 male, with a mean age of 58.9years. Nystagmus was recorded using an infrared camera and the findings were converted to digital data. Using ImageJ, we performed three-dimensional video-oculography and measured the maximum slow-phase velocity (MSV) of three components.
  
  
  RESULTS
  In the horizontal component, the mean value of MSV in the head-hanging position was 3°/s, and that in the nose-down position was 2.7°/s. There was no significant difference between the two positions. In the vertical component, the mean value of MSV in the head-hanging position was 4.3°/s, and that in the nose-down position was 6°/s. There was no significant difference between the two positions. In the torsional component, the mean value of MSV in the head-hanging position was 4.4°/s, and that in the nose-down position was 1.4°/s. The former was significantly greater than the latter (p<0.01).
  
  
  CONCLUSIONS
  Although we could not confirm the validity of Ewald's third law, the torsional component in the head-hanging position was significantly greater than that in the nose-down position.
authors.affiliation: Ichijo Ear, Nose and Throat Clinic, Hirosaki, Japan. hiro3387@mvj.biglobe.ne.jp
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ichijo
mesh_terms: D000328:Adult; D000368:Aged; D002137:Calculi / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D004584:Electronystagmography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007759:Labyrinth Diseases / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009759:Nystagmus, Pathologic / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D011187:Posture; D012027:Reflex, Vestibulo-Ocular; D012189:Retrospective Studies; D012665:Semicircular Canals / Q000503:physiopathology*; D014724:Vestibular Function Tests