Transtympanic versus tympanic membrane electrocochleography in examining cochleovestibular disorders

The use of electrocochleography (EcoG) is considered to be of clinical valu e in otological diagnosis. Non-invasive ear canal (EC) and tympanic membran e (TM) EcoG recording techniques, and invasive transtympanic (TT) technique are the methods used for objective assessment of cochlear function. In thi s study, eight adults (16 ears) with suspected Meniere's disease were exami ned using a newly designed, disposable tympanic electrode and a traditional , thin transtympanic needle. The amplitudes of the TT electrode responses w ere 4-6-fold larger than those produced by the TM electrode. The morphology of the waveforms for the two recording techniques was nearly identical. Th e mean amplitudes of the action potential (AP) obtained with the TM electro de were 2.39-3.73 mu V, and with the TT electrode 14.08-19.60 mu V, dependi ng on the stimulus intensity. For the summating potential (SP), the TM and TT electrodes had mean amplitudes of 0.82-1.60 mu V and 3.53-5.81 mu V, res pectively. 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 exa mination, since it was quite painless, unlike the TM examination. The autho rs recommend the use of the TT recording technique as a painless examinatio n in which the electrode is close to the inner ear, allowing a good signal- to-noise ratio and large amplitudes. Diagnostic interpretations art: easier and more reliable with the TT electrode than with the TM electrode.