Chapter 5 - Types of Hearing Loss

Abstract

Peripheral hearing loss comes in two broad types, conductive and sensorineural. We describe a diagnostic framework, which includes wideband acoustic immittance and middle ear muscle reflex combined with otoacoustic emissions (OAEs) and auditory brainstem responses. Acoustic trauma causes retrograde degeneration of auditory nerve fibers. It could be secondary when it follows inner hair cell (IHC) loss or primary as a result of damage of specific ribbon synapses in the IHCs. This primary degeneration can lead to “hidden hearing loss,” characterized by normal audiograms and OAEs but great difficulty in understanding speech, especially in background noise. Sensorineural hearing loss is accompanied by loudness recruitment, which often coexists with hyperacusis, and so can lead to “over recruitment.” Auditory neuropathy, only identified a two decades ago, is expressed as an auditory temporal processing disorders and has a strong genetic component. Cochlear implantation very often solves this problem. Ménière’s disease characterized by intermittent spontaneous attacks of vertigo, fluctuating sensorineural hearing loss, aural fullness or pressure, and roaring tinnitus still remains a mystery. We describe its natural history and the use of electrocochleography in detail. We conclude with age-related hearing impairment and describe the epidemiology and its peripheral and cortical substrates.