Transtympanic versus tympanic membrane electrocochleography in examining cochleovestibular disorders

The use of electrocochleography (EcoG) is considered to be of clinical value in otological diagnosis. Non-invasive ear canal (EC) and tympanic membrane (TM) EcoG recording techniques, and invasive transtympanic (TT) technique are the methods used for objective assessment of cochlear function. In this study, eight adults (16 ears) with suspected Meniere's disease were examined using a newly designed, disposable tympanic electrode and a traditional, thin transtympanic needle. The amplitudes of the TT electrode responses were 4-6-fold larger than those produced by the TM electrode. The morphology of the waveforms for the two recording techniques was nearly identical. The mean amplitudes of the action potential (AP) obtained with the TM electrode were 2.39-3.73 microV, and with the TT electrode 14.08-19.60 microV, depending on the stimulus intensity. For the summating potential (SP), the TM and TT electrodes had mean amplitudes of 0.82-1.60 microV and 3.53-5.81 microV respectively. The SP/AP ratios were larger with the TM electrode than with the TT electrode. They were inconsistent in four ears (25%) when measured with the TM and TT electrodes. All patients were more satisfied with the TT examination, since it was quite painless, unlike the TM examination. The authors recommend the use of the TT recording technique as a painless examination in which the electrode is close to the inner ear, allowing a good signal-to-noise ratio and large amplitudes. Diagnostic interpretations are easier and more reliable with the TT electrode than with the TM electrode.