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.
Keywords:
Electrocochleography - endolymphatic hydrops - Meniere's disease - cochlear microphonic
- summating potential - compound action potential - sensorineural hearing loss
