SeminarPresbycusis
Introduction
Presbycusis, literally elder hearing, is the general term applied to age-related hearing loss. The term encompasses all conditions that lead to hearing loss in elderly people.1 The disorder is characterised by reduced hearing sensitivity and speech understanding in noisy environments, slowed central processing of acoustic information, and impaired localisation of sound sources. As a result, people with the disorder have difficulty, proportional to the degree of hearing impairment, in conversation, music appreciation, orientation to alarms, and participation in social activities. There are three classic types of the disorder—sensory, strial, and neural—that can occur alone or in combination. Each type has implications for treatment.
Because of the high prevalence of presbycusis, hearing difficulty is a common social and health problem. Overall, 10% of the population has a hearing loss great enough to impair communication, and this rate increases to 40% in the population older than 65 years.2 80% of hearing loss cases occur in elderly people.3 Although hearing worsens with age, the severity of the hearing problem at any given age varies greatly. It is rare to find a person older than 70 years with no hearing impairment or whose hearing sensitivity has not declined from youthful levels. Hearing levels are poorer in industrialised societies4 than in isolated or agrarian societies.5 Thus, it is conceptually useful to regard presbycusis as a mixture of acquired auditory stresses, trauma, and otological diseases superimposed upon an intrinsic, genetically controlled, ageing process.
Presbycusis first reduces the ability to understand speech and, later, the ability to detect, identify, and localise sounds. The loss of hearing sensitivity begins in the highest frequencies, which has an adverse effect on understanding speech in noisy or reverberant places. Once the loss progresses to the 2–4 kHz range, which is important in understanding the voiceless consonants (t, p, k, f, s, and ch), speech understanding in any situation is affected. The most common complaint in presbycusis is not that the patient cannot hear, but rather that they cannot understand what is being said. For example, people will confuse “mash”, “math”, “map”, and “mat”, or “Sunday” with “someday”. Even such minor misperceptions, left uncorrected, can lead to communication errors or worse. The hearing loss extends to the lower frequencies with time resulting in poor speech detection as well as poor speech understanding. High-frequency warning sounds, such as beepers, turn signals, and escaping steam, are not heard or localised, with potentially disastrous results.
Hearing loss affects an individual's psychosocial situation. Untreated hearing impairment contributes to social isolation, depression, and loss of self-esteem. Hearing impairment has also been implicated as a cofactor in senile dementia,6 although others have contested this association.7 Many people regard presbycusis as an inevitable rite of passage into their senior years and are reluctant to seek help because of cost, vanity, and inconvenience. Others may ascribe their problem to mumbling speakers; for these people, recognition and acceptance of an age-related impairment is a difficult psychological hurdle.
Presbycusis management consumes an increasing portion of healthcare expenditures given the rising mean age of people in industrialised societies. Modern hearing aids are valuable aids to communication. Although they cannot restore lost sensory cells, they do provide acoustic power for declining metabolic function. On the horizon are investigations of treatment modalities that might correct the pathophysiological deficits of presbycusis and other hearing disorders. Such modalities will need more accurate diagnosis at the cellular level and greater medical involvement in their use than at present. The primary management of people with presbycusis in most communities is done by those who sell hearing aids. Only about 20% of people who might benefit from amplification have actually purchased an aid8, 9 and 25–40% either underuse or abandon hearing aid use.10, 11 Thus new treatment and management strategies need to be examined.
We review herein the structure and function of the ear, the altered functions in presbycusis, diagnostic considerations, and treatment options. We attempt to clarify important issues related to the causes of presbycusis and highlight what the practising physician could do to advise patients about the diagnosis, prevention, and treatment of the disorder. Finally, we point out areas of controversy and misunderstanding of the disorder and its treatment, and mention emerging research that could alter the treatment landscape of this highly common problem. In general, knowledge about presbycusis comes from animal models, clinical experience, human temporal bone research, and epidemiological studies. We have drawn from all these sources and have relied upon our extensive personal reference databases for this review.
Section snippets
Definitions
Presbycusis (or presbyacusis) is a general term that refers to hearing loss in the elderly and, as such, represents the contributions of a lifetime of insults to the auditory system. Of these, ageing and noise damage are the chief factors, plus genetic susceptibility, otological disorders, and exposures to ototoxic agents. Some people refer to presbycusis as hearing loss due solely to ageing. Because it is very difficult to isolate age effects from other contributors to age-related hearing
Anatomy and physiology
The external ear comprises the pinna and external auditory canal, which acts as a resonator and enhances sound transmission. The middle ear transforms air vibrations into the fluid-filled inner ear (cochlea) providing a pressure gain of 25–30 dB. The frequency range of human hearing is from 20 Hz to 20 kHz. Although the structures of the middle ear undergo age-related changes, there is very little effect, if any, on their function,12 with the notable exception of cerumen production, which seems
History
Hearing loss is often a silent disorder, characterised more by what is missed than what is heard. In many cases, family and friends are more aware of the problem than the patient. Nonetheless, most people with presbycusis will respond to a direct inquiry with a positive answer. People with depression and cognitive dysfunction should be assessed to exclude occult hearing loss as a contributing factor. The hearing loss is often accompanied by tinnitus—the perception of a ringing sound in the ears
Treatment
Hearing loss of all types affects not only communication but also quality of life. Mulrow and co-workers51 studied the effect of amplification on older patients with hearing loss and documented a positive effect of personal amplification (hearing aids) on quality of life.51 Therefore, treatment effects extend beyond communication. No treatment exists now to restore lost hearing. Research into hearing restoration is a growing scientific field.
Prevention
Although some degree of sensory presbycusis is inevitable, the deterioration can be reduced by avoidance of hazardous noise exposure or use of suitable hearing protection. Insert ear plugs provide about 15–25 dB of attenuation and can thus permit people to work in otherwise hazardous areas. The effects of noise accumulate over a lifetime; gun shooting and loud music exposure during adolescence will contribute to communication difficulties during the retirement years.
Cardiovascular disease and
Communication courtesy
Communication is a two-way process; the burden of communication falls equally on the speaker and listener. Common courtesy holds that both should work at improving the communication environment as well as the process when one of them has a hearing problem. The speaker should: be face-to-face with the listener, speak clearly and unhurriedly, turn off competing sound sources (TV, radio), and make sure that the message was received. The hearing-impaired listener should also be serious about
Cochlear implants
Cochlear implants are indicated at any age for people with bilateral severe hearing losses not materially helped by hearing aids. Current criteria include hearing no better than identifying 50% or fewer key words in test sentences in the best aided condition in the worst ear and 60% in the better ear. People of retirement age generally are excellent implant candidates since language skills are good and duration of deafness is short. Surgical morbidity is low and acceptance is high.
Conclusions
Presbycusis is common. The disorder deprives older people of key sensory input, which seriously affects their quality of life. Modern rehabilitation strategies are effective but underused. Primary physicians, especially those who care for elderly people, should consider the effect of presbycusis on health. Improvement in general health occurs after auditory rehabilitation.51 Recent evidence suggests that hearing loss may be an early sign of, as well as a contributor to, dementia.47 Screening
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