A review of electrocochleography: instrumentation settings and meta-analysis of criteria for diagnosis of endolymphatic hydrops.

This paper reviews the literature on instrumentation settings used for transtympanic (TT-ECOG) an extratympanic electrocochleography (ET-ECOG). There is wide variation regard to the applied stimulus, the settings and interpretation of ECOG results. For most physicians, the presence of endolymphatic hydrops is indicated either by the summating/action potential (SP/AP) ratio for click stimuli or the SP amplitude after tone bursts. Different upper limits have been proposed to discriminate hydropic from non-hydropic ears. Based upon a meta-analysis and classification criteria obtained from multivariate statistics, the authors propose that an SP/AP ratio with click stimulation > 0.35 using TT-ECOG, or > 0.42 using ET-ECOG, is indicative of hydrops. With tone burst stimulation set at a repetition rate of 30-40 stimuli per second, a SP of < -2 microV using TT-ECOG for at least one frequency within the range 0.5-8.0 kHz is considered pathologic.