title: Salt-load electrocochleography.
abstract: OBJECTIVE
  To introduce a new protocol for diagnostic electrocochleography using a pretest oral salt load to improve test sensitivity in patients with suspected inner ear fluid imbalance.
  
  
  METHODS
  A retrospective review of patients who reported vertigo that, by medical history, was suggestive of an inner ear fluid imbalance was preformed. The patients received a complete audiovestibular evaluation that included a baseline electrocochleogram. Despite the incapacitating nature of their vertigo, there were no symptoms or electrophysiologic abnormalities that would isolate an etiologic ear. After the baseline studies, the patients received 4 g of sodium chloride daily for 3 days before repeat electrocochleography. A control group of 13 healthy volunteers with normal baseline electrocochleography and pure tone audiometry was tested under similar conditions.
  
  
  METHODS
  This study was conducted at an ambulatory care clinic associated with a tertiary referral medical center.
  
  
  METHODS
  Electrocochleography was performed using alternating polarity clicks presented at a rate of 9.7/sec at 95 dB nHL by an extratympanic TIPtrode electrode and recorded with a Nicolet Spirit (Nicolet Instrument Corp., Madison, WI, U.S.A.). Responses were averaged for 1000 sweeps using a 10-msec time base with bandpass filtering from 5 to 1500 Hz. A summating potential/action potential (SP/AP) ratio of 0.37 was considered the upper limit of normal.
  
  
  METHODS
  Enhancement in the SP/AP ratio from a normal baseline value to > 0.37 after oral salt loading was indicative of a positive test.
  
  
  RESULTS
  None of the ears from control subjects had a positive salt load electrocochleogram, and one or both ears in 38% of the patients in the study group with normal baseline SP/AP ratios and symptoms of inner ear fluid imbalance converted to abnormal. The mean SP/AP ratio of the control group for the conditions before and after salt-load was not statistically different (p = 0.48), although the difference in the mean SP/AP ratio in the study group after salt loading was statistically significant (p = 1.329 x 10(-5)).
  
  
  CONCLUSIONS
  A group of patients who reported vertigo with no localizing abnormalities had a statistically significant increase in the mean SP/AP ratio after ingestion of a large quantity of sodium chloride. A modest percentage had elevation of the SP/AP ratio above the upper limit of normal for our audiovestibular lab. The localization of a "salt-senstitive" ear could assist the clinician in the management of these difficult problems with long-term medical therapy or surgical treatment when alternative measures fail.
authors.affiliation: The University of Texas Southwestern Medical Center, Dallas 75235, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Gamble
authors.forename: W L
authors.initials: WL
authors.lastname: Meyerhoff
authors.forename: A G
authors.initials: AG
authors.lastname: Shoup
authors.forename: N D
authors.initials: ND
authors.lastname: Schwade
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001300:Audiometry, Evoked Response / Q000379:methods*; D005260:Female; D006801:Humans; D007761:Labyrinthine Fluids / Q000378:metabolism*; D008575:Meniere Disease / Q000175:diagnosis* / Q000601:surgery; D008875:Middle Aged; D012189:Retrospective Studies; D012720:Severity of Illness Index; D012965:Sodium Chloride / Q000493:pharmacokinetics*; D016896:Treatment Outcome; D014725:Vestibular Nerve / Q000601:surgery
chemical_list: D012965:Sodium Chloride