title: Hyperventilation-induced nystagmus in patients with vestibular schwannoma.
abstract: OBJECTIVE
  To determine the utility of the hyperventilation test (HVT) in the diagnosis of vestibular schwannoma (VS).
  
  
  METHODS
  A retrospective analysis of hyperventilation-induced nystagmus (HVIN) in 45 patients with unilateral VS.
  
  
  METHODS
  A tertiary referral center.
  
  
  METHODS
  Forty-five patients with VS; 30 patients with chronic vestibular neuritis; 20 healthy subjects with normal hearing and without symptoms or a history of vertigo, migraine, or neurological diseases (control group).
  
  
  METHODS
  Audiological and vestibular examination; "side-stream" measurement of end-tidal CO2 pressure (P(EtCO2)) to standardize the procedure; magnetic resonance imaging (MRI) centered on the cerebellopontine angle.
  
  
  METHODS
  An analysis of HVIN, its patterns, and its appearance threshold via the measurement of P(EtCO2) correlations with the tumor size.
  
  
  RESULTS
  HVIN was observed in 40 of 45 cases (88.9%) in the schwannoma group and in 12 of 30 cases (40%) in the chronic vestibular neuritis group; HVIN was not observed in the control group (0/20 cases) (p < 0.001). In the schwannoma group, HVIN was evoked at a mean P(EtCO2) value of 16.5 ± 1.15 mm Hg. The hypofunctional labyrinth was identified with high sensibility and specificity through caloric test, head shaking test, and head thrust test. The excitatory pattern, which included HVIN with slow phases that beat toward the hypofunctional side, and the paretic pattern, which included HVIN with slow phases that beat toward the hypofunctional side, were not significantly associated with VS size (19.04 ± 10.56 mm for the excitatory pattern and 19.06 ± 11.01 mm for the paretic pattern). The difference in the VS size in HVIN+ (19.05 ± 10.60 mm) and HVIN- (8.40 ± 2.19 mm) cases was significant (p = 0.009).
  
  
  CONCLUSIONS
  A 60-second hyperventilation event causes metabolic changes in the vestibular system and reveals a latent vestibular asymmetry. The presence of an excitatory pattern is the major criterion that suggests VS in patients with signs of unilateral vestibular deficit.
authors.affiliation: Department of Audiology and Phoniatrics, "G. Rummo" Hospital, Benevento, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Califano
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Iorio
authors.forename: Francesca
authors.initials: F
authors.lastname: Salafia
authors.forename: Salvatore
authors.initials: S
authors.lastname: Mazzone
authors.forename: Maria
authors.initials: M
authors.lastname: Califano
mesh_terms: D002530:Cerebellopontine Angle / Q000473:pathology; D003937:Diagnosis, Differential; D006801:Humans; D006985:Hyperventilation / Q000150:complications* / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D009464:Neuroma, Acoustic / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology; D009759:Nystagmus, Pathologic / Q000209:etiology* / Q000503:physiopathology; D012189:Retrospective Studies; D014724:Vestibular Function Tests; D020338:Vestibular Neuronitis / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology