Transtympanic electrocochleography: a 10-year experience.

Abstract

To report the authors' experience with transtympanic electrocochleography during the past 10 years. Retrospective case review. Otology/neurotology referral center. Transtympanic electrocochleography was performed on 2,421 ears of 2,140 patients from May 1990 to April 2000. Clicks and tonebursts were used in electrocochleography testing. Summating potential/action potential ratio was calculated. Action potential latency shift by rarefaction and condensation clicks was measured. Cochlear microphonic was recorded. An enlarged summating potential/action potential ratio (>0.40), broadened action potential waveform (>3 msec) or prolonged action potential latency shift (>0.2 msec) was considered to be indicative of endolymphatic hydrops. The presence of cochlear microphonic indicated hair cell survival. In response to clicks, an enlarged summating potential/action potential ratio was found in 76.1% of ears and a broadened action potential waveform in 70%. Either an enlarged summating potential/action potential ratio or a broadened action potential waveform was observed in 78.4% of ears. In response to tonebursts, an enlarged summating potential/action potential ratio was found in 64.8%. The combined use of clicks and tonebursts yielded an enlarged summating potential/action potential ratio in 81.7%. Electrocochleography using tonebursts had the advantage of frequency selectivity. A prolonged action potential latency shift was found in 62.2% of ears with Ménière's disease. A significant association between an enlarged summating potential/action potential ratio and an action potential latency shift was noted (chi = 5.357, p = 0.021). An enlarged summating potential/action potential ratio was found 71% in Stage 1 of Ménière's disease, 82% in Stage 2, 85% in Stage 3, and 90% in Stage 4 (chi = 19.442, p = 0.000). An enlarged summating potential/action potential ratio was associated with the duration of the disease, 43% in the under 1-year group, and 100% in the more than 30-years group (chi = 33.555, p = 0.000). A large cochlear microphonic was present in 69% of ears with hearing levels greater than 40 dB. Transtympanic electrocochleography using clicks and tonebursts is a reliable test to detect the presence of endolymphatic hydrops in Ménière's disease. A prolonged action potential latency shift evoked by rarefaction and condensation clicks is a useful addition to the application of electrocochleography in the diagnosis of Ménière's disease.