title: Functional significance of peripheral head-shaking nystagmus.
abstract: OBJECTIVE
  The objective was to determine the characteristics of horizontal head-shaking nystagmus of peripheral origin and its relationship to vestibular dysfunction.
  
  
  METHODS
  Retrospective case series.
  
  
  METHODS
  Eighty-three patients met the inclusion criteria of having peripheral and unilateral vestibular disease. Patients were tested with video nystagmography. Head-shaking nystagmus was performed in the horizontal plane during 30 cycles at a frequency of approximately 3 Hz. Head-shaking nystagmus was classified as monophasic or biphasic and, based on the pathological ear, as ipsilateral or contralateral related to nystagmus fast phases. The two-tailed t test, ANOVA, Mann-Whitney and chi2 tests, and lineal and polynomial regression tests were used for statistical analysis.
  
  
  RESULTS
  Twenty-three patients showed a positive head-shaking nystagmus. All cases of head-shaking nystagmus observed were horizontal. There were four biphasic and 19 monophasic cases of head-shaking nystagmus. First phases of biphasic head-shaking nystagmus beat toward the normal ear. Eleven of the monophasic cases of head-shaking nystagmus were ipsilateral, and nine were contralateral. There was a statistically significant correlation between caloric weakness and head-shaking nystagmus. Ipsilateral head-shaking nystagmus corresponded to lower caloric asymmetries, and contralateral and biphasic head-shaking nystagmus corresponded to greater caloric weakness (P <.001). As the caloric asymmetry increased, the maximal slow-phase eye velocity of head-shaking nystagmus was greater (P =.01) and its duration shortened (P =.008). Ipsilateral responses could be distinguished from contralateral responses based on their latency (P =.03), maximal slow-phase eye velocity (P <.05), and duration (P =.02). The frequency of head-shaking nystagmus was significantly higher among older patients. There was no correlation between head-shaking nystagmus and clinical patterns.
  
  
  CONCLUSIONS
  Head-shaking nystagmus of peripheral vestibular origin is a response both qualitatively and quantitatively associated with the degree of the vestibular loss.
authors.affiliation: Department of Otolaryngology, Hospital Carmen y Severo Ochoa, Cangas del Narcea , Spain. pperez@medynet.com
authors.forename: Paz
authors.initials: P
authors.lastname: Pérez
authors.forename: José Luis
authors.initials: JL
authors.lastname: Llorente
authors.forename: Justo R
authors.initials: JR
authors.lastname: Gómez
authors.forename: Alfredo
authors.initials: A
authors.lastname: Del Campo
authors.forename: Aurora
authors.initials: A
authors.lastname: López
authors.forename: Carlos
authors.initials: C
authors.lastname: Suárez
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D004584:Electronystagmography; D005260:Female; D006257:Head / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009759:Nystagmus, Pathologic / Q000209:etiology / Q000503:physiopathology*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D015837:Vestibular Diseases / Q000150:complications / Q000503:physiopathology*