Ninety percent of patients older than 80 years cope with difficulty in hearing conversations, instructions, or sounds that enrich, orient, or protect them. Hearing loss is in fact the third most common chronic condition of aging, following arthritis and hypertension.¹ The condition is more than a minor inconvenience. It contributes to impaired cognitive function, significant social and emotional handicap, and loss of independence.

This chapter reviews the etiology of hearing loss resulting from environmental insults and physiologic changes in the ear in response to aging (i.e., presbycusis or impaired audition in aging). Practical techniques for detecting hearing loss in the clinician’s office and interpreting common diagnostic tests typically performed by audiologists are presented in conjunction with strategies for treatment, rehabilitation, and selection of assistive devices from the array of options on the market. Also included is a discussion of tinnitus, a frustrating hearing condition for both patients and their clinicians and its companion, vertigo.

A common prop in caricatures of frail, feisty, wrinkled, stooped old folks is a ram’s horn strategically held next to the ear to capture sound. The image reflects behaviors that are symptomatic of impaired audition: Turning up the volume on the television or radio, speaking loudly, misinterpreting words, or disengaging from group discussions. However, hearing decline begins in the fourth decade. The extent and causes of hearing loss vary considerably across individuals; however, large cohort studies in Framingham, Wisconsin, Baltimore, Venice, Gothenburg (Germany), Denmark, and the United Kingdom consistently document the prevalence of the problem. Overall prevalence of hearing loss in a cohort of 3,753 persons aged between 48 and 92 years in the Beaver Dam, Wisconsin, study was estimated to be 45.9%.² Hearing declines at the rate of 0.5 to 0.7 dB per year for highpitched sounds (i.e., frequencies of 2 to 4 kHz). This rate of decline quadruples in the seventh decade, particularly among men. Although this may vindicate those accused of “wife deafness,” the gender gap virtually disappears by the ninth decade. According to Schuknecht,³ there are multiple patterns, and therefore multiple underlying structural patterns, of age-related hearing loss, including sensory, neural, strial, and cochlear-conductive forms of presbycusis.

Human hearing translates vibrations into identifiable sounds ranging from the subtle drip of a leaky faucet to the startling clap of nearby thunder. The brain uses the difference in timing and level of signals arriving from a pair of ears to reliably locate the source of sound. Mechanical sound waves are captured by the saucer-shaped outer ear and travel through the auditory canal to the flexible eardrum (tympanic membrane [TM]) (see Fig. 12.1). The resulting vibration is transmitted to the first of three linked bones or ossicles in the middle ear: The malleus, incus, and stapes. The stapes, resembling a saddle, inserts into the oval window of the inner ear’s cochlea. Because this membrane is much smaller than the eardrum and because the ossicles multiply incoming forces by their combined mechanical advantage, the pressure exerted on the cochlea is approximately 20 times stronger than that on the TM.⁴ The cochlea, bearing a striking resemblance to the shell of the chambered nautilus, is filled with fluid. Specialized hair cells in the inner ear (cochlea), organ of Corti, pick up the transmitted cadence, opening up ion channels when the hairs (stereocilia) bend and leading to an intracellular depolarization. This completes the conversion of mechanical energy to electrical energy and leads to the release of neurotransmitters. The auditory branch of the eighth cranial nerve projects onto the cochlear nuclei, through the auditory brainstem to the medial geniculate body of the metathalamus, and, finally, to the primary auditory cortex of the temporal lobe. The cochlea also intercepts vibrations directly from surrounding bone, which serves as the basis for bone-conduction thresholds used audiometrically.

With age, alterations in the peripheral receptive organ contribute to presbycusis. Elasticity diminishes in the cartilage of the outer ear. Reduced numbers of active sebaceous glands produce drier and less viscous cerumen that is prone to obstruct the external auditory canal. Mechanical transmission of sound is affected by decreased elasticity, thinning of the TM, and calcification of the
joints between the middle ear ossicles. The inner ear’s organ of Corti, however, is most susceptible to age-related changes. The stria vascularis may atrophy. This network of endolymph-secreting capillaries generates a resting potential (called the endolymphatic potential) that sensitizes the hair cells in the cochlea.⁵ Hair cell loss, most severe in the basal or high-frequency region of the cochlea, is responsible for the decline in pure-tone hearing in conjunction with loss of ganglion cells and reduction in fibers in the cochlear nerve. Hearing is also contingent on timely and accurate interpretation of information from the environment. Processing information in the temporal lobe may be affected by reduction in neuron number, size, or dendritic arborization.

Hearing deficits are categorized as conductive, sensorineural, or retrocochlear. A conductive hearing loss locates the problem to the middle or external ear. A sensorineural loss stems from inner ear structures (primarily the stria vascularis and cochlear hair cells). A retrocochlear loss involves portions of the auditory system that involve the eighth cranial nerve or central auditory nervous system. Once localized, the differential diagnosis includes age-related structural changes (i.e., impacted cerumen, tympanosclerosis, cochlear hair cell loss), infections, tumors, trauma, noise or other toxic exposures, genetic traits and congenital malformations. Tinnitus, often associated with hearing loss, is a troubling condition caused by the perception of sounds without an external source. Table 12.1 lists some conditions that are associated with hearing difficulty.

This woman would be a good candidate for a hearing aid because her hearing loss in the lower frequencies is sufficient to make it difficult to hear speech at conversational levels and her speech discrimination in quiet is excellent.