title: Persistent geotropic direction-changing positional nystagmus with a null plane: the light cupula.
abstract: OBJECTIVE
  The aim of this study was to characterize the clinical features and typical positional nystagmus in patients with persistent geotropic direction-changing positional nystagmus (DCPN) and address the possible pathophysiology of the disease. Furthermore, the proportion of light cupula among the patients showing geotropic DCPN was investigated to assume the incidence of light cupula in those patients.
  
  
  METHODS
  Prospective case series.
  
  
  METHODS
  We conducted a prospective case series study in 19 patients with persistent geotropic DCPN. Positional nystagmus during the bow and lean test and the supine head roll test was analyzed using videonystagmography.
  
  
  RESULTS
  All of the 19 patients showed persistent geotropic DCPN without latency. A null plane in which the nystagmus ceases was identified in all of 19 patients, and the intensity of nystagmus was stronger on one side in13 patients (68%) on supine head roll test. Overall, the affected side could be identified in 18 patients (95%). About 14.2% (19 of 134) of patients with geotropic DCPN could be diagnosed as having light cupula in the horizontal semicircular canal.
  
  
  CONCLUSIONS
  The patients with light cupula show persistent geotropic DCPN without latency. Affected side(s) can be determined by the direction and intensity of the characteristic positional nystagmus and the side of the null plane. The pathophysiology and treatment of light cupula still remain to be elucidated.
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine.
authors.forename: Chang-Hee
authors.initials: CH
authors.lastname: Kim
authors.forename: Min-Beom
authors.initials: MB
authors.lastname: Kim
authors.forename: Jae Ho
authors.initials: JH
authors.lastname: Ban
mesh_terms: D000328:Adult; D000368:Aged; D053483:Eye Movement Measurements; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009759:Nystagmus, Pathologic / Q000503:physiopathology*; D011446:Prospective Studies
keywords: Benign paroxysmal positional vertigo; direction-changing positional nystagmus; geotropic nystagmus; head roll test; null plane