Chapter 55: The Aging Inner Ear

INTRODUCTION

GENERAL CONSIDERATIONS

The world’s older population is growing at an unprecedented rate. According to the National Institutes of Health, 8.5% of the world (617 million) is age 65 and older. By 2050, this percentage is estimated to be 17% (1.6 billion). Consequently, the prevalence of age-related auditory and vestibular dysfunction will increase.

Like other organ systems, the inner ear undergoes degenerative changes with aging. Genetic and environmental factors result in variable functional disability. In the United States, hearing difficulty is reported by one-third of people in the age group of 65 to 70 years and by nearly half of those over 75 years of age. It has been estimated that between 1.5% and 3.0% of the total population would benefit from hearing aids. However, hearing aids are underutilized amongst the elderly, with an estimated 14.2% of Americans who would benefit from hearing aids actually using them.

Vestibular dysfunction is also common in the elderly, with reported prevalence of vertigo, disequilibrium, or imbalance in up to half of men and two-thirds of women over the age of 70 years. The incidence of falling in these individuals is estimated to be up to 40% in those living at home and is twice as frequent for the institutionalized elderly. These falls are associated with significant morbidity and mortality and constitute one of the leading causes of death among the elderly.

The specialized neural cells of the auditory and vestibular systems are nonmitotic and thus cannot undergo replication and renewal. Over a lifetime, cellular damage, environmental exposures (eg, noise, ototoxic substances), and genetic susceptibilities all contribute to the degree of age-related hearing loss and vestibular dysfunction.

PATHOGENESIS

A. Age-Related Hearing Loss

Hearing loss in the elderly is multifactorial and is due to the convergence of various risk factors. Presbycusis is the otherwise unexplained, slowly progressive, predominantly high-frequency symmetric hearing loss due to the aging process (Figure 55–1). Progressive high-frequency hearing loss has been clearly documented by numerous studies in populations over the age of 40 years (Figure 55–2A). Morphologic studies of human temporal bones have demonstrated an age-related loss of inner and outer hair cells and supporting cells, with the greatest loss being in the basal turn of the cochlea, which corresponds to higher frequencies.