ECochG

Electrocochleography (ECochG) is an electrophysiological test that records the electrical potentials generated in the cochlea and auditory nerve in response to acoustic stimulation. The recorded signals reflect activity from hair cells and neural elements, providing information about peripheral auditory function and cochlear health.

The main components of an ECochG signal are the cochlear microphonic (CM), the summating potential (SP), and the compound action potential (CAP). The CM is mainly produced by outer hair cells and mirrors the waveform of the stimulus. The SP reflects a sustained offset potential related to hair cell activity, while the CAP represents the synchronized firing of auditory nerve fibers at stimulus onset. Recordings can be obtained with noninvasive electrodes placed in the ear canal or on the forehead, or with invasive transtympanic needle electrodes that yield higher signal quality. Stimuli typically include clicks or tone bursts, and signals are amplified and averaged to improve detection.

Clinical uses include evaluation of cochlear health and diagnostic adjunct in suspected endolymphatic hydrops (Ménière's disease), where SP and CAP measures or their ratio can aid interpretation. ECochG is also used to monitor cochlear function during ototoxic drug therapy and during cochlear implant surgery, where intraoperative ECochG can help preserve residual hearing. It can assist in difficult-to-test patients or in research settings assessing frequency-specific cochlear function.

Limitations include small signal amplitudes, sensitivity to electrode placement and middle-ear status, and the need for specialized equipment and expertise. Results can be influenced by patient state, noise, and anesthetic factors, and interpretation is not universally standardized across clinics.