Electrocochleography

Abstract

Electrocochloeography (ECOG) is an electrophysiologic recording technique used for recording electrical responses from the cochlear and distal portion of the auditory nerve. It has been used for a variety of purposes, the most common clinical application being the diagnosis of endolymphatic hydrops. Three cochlear potentials can be observed on ECOG recordings. The cochlear microphonic (CM) is an AC potential that resembles the acoustic waveform of the evoking stimulus and is produced by cochlear hair cells. The summating potential (SP) is a DC potential that follows the waveform envelope of an acoustic stimulus and is also produced by cochlear hair cells. The SP is abnormally large in patients with active cochlear hydrops. The VIIIth Nerve Compound Action Potential (AP) is the summed activity of a group of synchronously discharging cochlear neurons, evoked by a transient stimulus. The electrode locations have been employed—extratympanic, tympanic, and transtympanic. Extratympanic recordings are not adequate for detecting abnormal summating potentials. Transtympanic electrodes provide excellent recordings but require an invasive procedure. Tympanic recordings are usually adequate for obtaining reliable recordings of cochlear potentials evoked by relatively high intensity acoustic stimuli. Meniere's disease is viewed to be a fluctuating progressive condition in which cochlear potentials are affected differently at different stages of the disease. In early stages, ECOG is helpful for distinguishing Meniere's disease from non-hydropic forms of hearing loss and dizziness.