Salt-Load Electrocochleography

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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.

Study Design:

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.

Setting:

This study was conducted at an ambulatory care clinic associated with a tertiary referral medical center.

Intervention:

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 Instalment 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.

Main Outcome Measures:

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 SPsol;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 SPsol;AP ratio in the study group after salt loading was statistically significant (p=1.329 × 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 longterm medical therapy or surgical treatment when alternative measures fail.

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