Hearing Loss

Geriatric Essentials

• Presbycusis (age-related, gradual, bilateral, symmetric, and predominantly high-frequency hearing loss) is the most common form of hearing loss in the elderly.
• All elderly people should be screened at least annually for hearing loss.
• Treatment of hearing loss with well-fitted hearing aids, assistive listening devices, and aural rehabilitation improves function and quality of life.

In the US, about 10% of the population has hearing loss; half of those affected are >= 65. About 1 of 3 people age 65 to 75 and 1 of 2 > 75 have hearing loss, making hearing loss the most common disability among the elderly.

Hearing loss impairs communication and can socially isolate affected people from their family members and friends. Hearing loss can also cause or aggravate depression, anxiety, and feelings of inadequacy, contributing to functional impairment.

Etiology

Hearing loss that occurs due to aging is called presbycusis. Presbycusis is the most common form of hearing loss among the elderly. Four types have been described. Sensory presbycusis is loss of cochlear hair cells and subsequent degeneration of associated neurons. Neural presbycusis is primary degeneration of cochlear neurons and the auditory nerve. Metabolic presbycusis is degeneration of the stria vascularis, which contains the cochlea's blood supply. Mechanical (cochlear conductive) presbycusis is stiffening of the cochlea's basilar membrane. Most patients have a combination of neural and metabolic presbycusis.

There are many other, less common causes of hearing loss among the elderly (see Table 128-1).

Hearing loss may be classified as sensorineural, conductive, mixed, or retrocochlear. Sensorineural hearing loss, which includes presbycusis, involves damage to the hair cells of the cochlea (sensory hearing loss), the 8th cranial nerve (neural hearing loss), or both. Conductive hearing loss is caused by a mechanical or physical blockage of sound. Mixed hearing loss includes the presence of both sensorineural and conductive hearing losses. Retrocochlear hearing loss refers to neural hearing loss that results from damage to parts of the auditory system other than the inner ear. Causes of retrocochlear neural hearing loss include tumors of the 8th cranial nerve, superficial hemosiderosis, and others rather than the benign loss of auditory neurons that occurs with most presbycusis.

Symptoms and Signs

Hearing loss may affect the hearing threshold (the volume at which a patient can hear sound, expressed in decibels [dB]), discrimination (the ability to differentiate among various speech sounds), or both. Different frequencies of sound (expressed in hertz [Hz]) may be affected. Hearing loss may affect one or both ears. It may affect the ears equally (symmetric) or unequally (asymmetric). Specific patterns of hearing loss and symptoms that can accompany hearing loss vary depending on the cause. Outer and middle ear causes result in conductive hearing loss; inner ear causes result in sensorineural hearing loss (see Table 128-1 for causes other than presbycusis).

Presbycusis: Presbycusis decreases the ability to hear high-frequency sounds. The decrease is gradual, bilateral, and symmetric. It most commonly manifests as gradual difficulty understanding what is heard despite reporting that speech and other sounds seem loud enough to hear. Affected patients may say that everyone mumbles. The patient's spouse or partner may report that the patient turns the television volume up very high and asks for words to be repeated. Patients may avoid social situations, religious services, and movie theaters. Music lovers may complain that music does not sound as bright.

Patients with presbycusis have difficulty understanding speech because their hearing is poorest for high-frequency sounds. In English, consonants, which are high-frequency sounds around 3000 to 4000 Hz, provide most of the clarity in speech. Consonant sounds (eg, "s," "sh," "f," "p," "t") are the most important sounds for speech recognition. For example, when "shoe," "blue," "true," "too," or "new" is spoken, many patients with presbycusis can hear the "oo" sound, but most have difficulty recognizing which word was spoken because they cannot distinguish the consonants. Tinnitus often accompanies presbycusis.

Diagnosis

Screening for hearing loss at least annually is strongly recommended for all elderly people, because they often hide their hearing loss, being embarrassed by it and equating it with aging. Also, those who have few social interactions may be unaware of mild hearing loss, placing them at risk of injury and further social isolation. When hearing loss is suspected, a history should be obtained and an otoscopic examination performed. Tuning fork tests may be useful. A complete audiometric evaluation should be performed by an audiologist.

Screening: (See also The Rand Corporation's Quality Indicators for the Management of Hearing Loss in Vulnerable Elder Persons.) One approach to screening is asking whether the patient is experiencing any problems with hearing. A standardized, validated questionnaire such as the Hearing Handicap Inventory for the Elderly can be used to screen for problems and the effects of hearing problems on function.

Patients can also be asked to repeat a short series of numbers or letters whispered by the examiner from arm's length behind the patient. The most sensitive and specific test uses a handheld device (such as a handheld audiometer) to test hearing at preset thresholds of 20, 25, and 40 dB, for frequencies of 500, 1000, 2000, and 4000 Hz.

History: The patient is asked when the hearing loss was first noticed, whether it has worsened with time, and whether hearing is about the same in both ears. The patient is asked about symptoms (eg, pain and tinnitus in either or both ears, aural drainage, episodic dizziness or vertigo), possible causes of hearing loss (eg, significant noise exposure, previous ear surgery, past and current use of ototoxic drugs), hearing aid use, and family history of hearing loss and hearing aid use.

Certain symptoms suggest a diagnosis other than presbycusis and require further evaluation by a physician. They include unilateral hearing loss, unilateral tinnitus, recent or abrupt changes in hearing, fluctuating hearing loss, aural pain, and aural drainage.

Otoscopic examination: Findings that may suggest a conductive hearing loss include drainage from an ear, cerumen occlusion, anomalies of the ear canal or tympanic membrane (eg, a perforation, tympanosclerosis, a red bulging tympanic membrane, a meniscus, amber fluid, bubbles), blood in the ear, unusual growths or lesions of the pinna or ear canal (eg, a glomus tumor), external otitis, and signs of a medically correctable hearing loss. About 85 to 95% of patients examined by an audiologist do not have such findings.

Tuning fork tests: The patient's ability to hear may be estimated with a 256-Hz or 512-Hz tuning fork. However, Rinne's and Weber's tuning fork tests yield limited information. Because tuning forks are not calibrated, they have different amplitudes when vibrating, potentially leading to erroneous results.

Rinne's test compares hearing by air conduction (the normal route of sound transmission-through the ear canal, tympanic membrane, and ossicles) to hearing by bone conduction. The center prong of a vibrating tuning fork is placed on the mastoid process (for bone conduction). Then the vibrating tuning fork is held about 2.5 cm from the pinna (for air conduction). If the mastoid presentation is louder, a conductive or mixed loss is suspected. If the pinna presentation is louder, hearing may be normal or a sensorineural or retrocochlear hearing loss may be present.

Weber's test evaluates hearing by bone conduction only. A vibrating tuning fork is placed on the front teeth, bridge of the nose, or center of the forehead. If the sound is louder in what the patient reports as being "the bad ear," the patient may have conductive or mixed hearing loss in that ear. If the sound is louder in what the patient reports as being "the good ear," the patient may have sensorineural hearing loss in that ear. If the sound is centered, hearing is normal or impairment is about the same in both ears.

Audiometry: The audiogram is a standardized tool for recording hearing thresholds at different frequencies (see Figure 128-1). It lists the frequencies (pitch) from left (low frequencies) to right (high frequencies) across the x-axis. Although humans can detect frequencies from about 20 to 20,000 Hz, the audiogram records the parts of the spectrum most important to human speech (250 to 8000 Hz, in octaves). Amplitudes (loudness) of sound are displayed from top (soft) to bottom (loud) along the y-axis. The audiogram usually records amplitudes from about -10 to 110 dB. The measurement may be negative (ie, better than normal) in some people because 0 dB represents the hearing threshold average for a group of people with normal hearing.

Typically, the degree of hearing loss is determined by averaging the pure tone hearing thresholds (in decibels) for 500, 1000, and 2000 Hz. The resulting number, the pure tone average, is used to define the degree of hearing loss.

A pure tone average <= 25 dB across the speech frequencies is considered normal hearing in adults. A pure tone average of 26 to 40 dB indicates mild hearing loss; 41 to 70 dB indicates moderate hearing loss; 71 to 90 dB indicates severe hearing loss; and >= 91 dB indicates profound hearing loss.

Speech audiometry: Although determining pure tone thresholds is important, most patients present with problems of speech perception, which pure tone testing does not directly evaluate. Speech audiometry evaluates how well a patient perceives speech sounds. The standard measures of speech perception are the speech reception threshold and the word recognition score.

The speech reception threshold is the lowest level (in decibels) at which the patient can accurately repeat 50% of a series of balanced 2-syllable words (eg, baseball, railroad, staircase). The speech reception threshold is usually within 5 dB of the pure tone average. Therefore, the speech reception threshold and the pure tone average can be used as checks for each other, validating the threshold responses.

The word recognition score represents the ability to maximally understand (ie, discriminate, hear clearly, recognize) speech sounds. It is measured by presenting phonetically balanced monosyllabic words (typically, a list of 25) at a comfortable loudness level for the patient. The words are presented using a carrier phrase (eg, "you will say 'boat,'" "you will say 'went'"). The patient is asked to repeat the final word. The score is the percentage of words repeated correctly. However, a score of 100% does not necessarily preclude the need for hearing aids. For example, if the score is 100% at a presentation level of 85 dB (which is louder than that of average conversational speech), the patient would almost certainly benefit from hearing aids.

Generally, speech recognition threshold and word recognition tests are performed using recordings to ensure reliability and to test each patient against the same task. When live voice tests are used, variation in signal loudness, accent, timing, and other factors can contaminate the test results to an unknown degree. Nonetheless, live voice tests are sometimes necessary-eg, for patients with Alzheimer's disease and those who have difficulty completing a task.

Among patients with presbycusis, the typical audiometric test result is a bilateral mild-to-moderate hearing loss. Hearing is usually best in low frequencies and poorest in high frequencies. Usually, the speech reception threshold is appropriate (within 5 dB of the pure tone average), and the word recognition score is > 80%.

Patients with auditory processing problems or cochlear or neural hearing loss may have a low word recognition score because their auditory system does not faithfully reproduce the clarity of speech, regardless of loudness. Patients with a score below about 70% have difficulty understanding conversational speech without visual cues, despite being able to hear sound.

Treatment

Although physicians diagnose hearing problems and medically and surgically treat appropriate patients, the majority of patients with hearing loss, including those with presbycusis, are managed by audiologists. They counsel and advise patients about hearing loss, recommend and fit hearing aids, help manage tinnitus, recommend ways to avoid noise problems, and recommend and supply assistive listening devices for patients requiring them. Audiologists can also provide aural rehabilitation services.

Hearing aids: The primary treatment for presbycusis, and for certain other causes of hearing loss, is hearing aids. However, < ½ of elderly people with hearing loss who might benefit from hearing aids actually wear them. There are many styles, and patients should choose a style that they will wear without embarrassment. Cosmetic concerns cannot be ignored in the fitting of hearing aids.

Patients with symmetric hearing loss usually need binaural (ie, both ears) hearing aids. About 80% of hearing aid wearers are now fitted binaurally. Binaural amplification enables the brain to compare and contrast sounds from both ears and to perceive amplitude and spectral and phase cues, which greatly improve speech recognition in quiet and noisy situations.

If patients with binaural hearing loss wear only one hearing aid, they cannot tell where a sound is coming from, and in difficult situations (eg, noisy ones), they cannot hear speech clearly. Additionally, more amplification is usually required with a monaural unit than with binaural units. A monaural hearing aid is used only if patients have financial constraints, if only one ear requires amplification (either because hearing loss in the other ear is unlikely to respond to amplification or hearing is normal), or if they have binaural interference. Binaural interference, thought to result from prolonged deprivation or age-related changes in the central auditory system, causes marked differences between ears in sound processing and awareness. For people with this relatively rare situation, 2 hearing aids may be worse than one.

Realistic expectations are key to successful treatment with hearing aids. Even the best hearing aids do not enable a patient to hear clearly in adverse listening situations, such as those involving poor acoustics (due to high reverberation), a poor signal-to-noise ratio (the intensity of speech in relation to the intensity of competing signals or background noise), excessive background noise, or poor visual contact between speaker and listener (eg, in poor lighting). Even with well-fitted hearing aids, patients usually need redundant and plentiful auditory and visual communication cues during normal discourse to maximize speech perception.

The basic components of a hearing aid include a microphone that converts sound into an electrical current, an amplifier that strengthens that current, a receiver, and a battery. Hearing aids, like most electronic devices, have benefited from advances in microprocessing. Hearing aids are now available that digitally adapt the output of the amplifier to the characteristics of the listening environment. Others use a remote, patient-operated control (some as a pen-shaped device that fits in a pocket or a wrist-watch remote) to tailor the response to the wearer's needs using preset programs.

Hearing aids are available in 3 basic technologies: analog (with traditional circuits), digitally programmable (an analog unit with digitally controllable parameters), and 100% digital (which has analog microphones and receivers, despite its name). Hearing aids can also be placed into 4 size categories: behind-the-ear, in-the-ear, in-the-canal, and completely-in-the-canal. Digitally programmable and digital hearing aids are used by about 83% of hearing aid wearers.

Analog hearing aids, the most common and least expensive type, make sound louder but provide the least amount of sound processing. Thus, they may be preferred by patients who need basic amplification at the lowest possible price. Analog units are available in all sizes. They can be manufactured with multiple screw-set controls (potentiometers) to adjust compression ratios and compression knee points (level at which compression is initiated), low- and high-frequency gain (amplification power), maximum output, and other parameters. Compression is the process by which sound is squeezed into a range of comfortable volumes. Thus, quiet sounds are made louder, but sounds above a certain volume are made quieter. An adjustable compression feature is particularly useful for patients with recruitment. Recruitment, a symptom of cochlear hair cell damage common in the elderly, makes certain pitches seem uncomfortably loud at levels that would be considered comfortable by people with normal hearing.

Digitally programmable hearing aids (digitally controlled analog units) are hybrids that enable the audiologist to control the hearing aid's characteristics with digital accuracy (using a computer) while delivering sound via analog technology. Control of the circuit is vastly improved, and these units can be tuned to the patient's preferences. They are available in all sizes. They vary in price but are usually more expensive than analog units.

Digital hearing aids (digital signal processing units) are the most technologically advanced. They are the size of a pencil eraser and fit inside the ear canal. These units can process speech at > 100 million calculations/sec and can use feedback control, directionality, noise reduction, and many processing strategies to maintain a comfortable listening level for all sounds-from very soft to very loud. They are available in all sizes and are the most expensive.

Behind-the-ear hearing aids are the most powerful ear-level units (see Figure 128-2). Because the receiver and microphone are separated, gain can be increased with less chance of acoustic feedback (whistling). Because this aid is relatively large, it can accommodate many circuit options (eg, telephone coils, direct audio input, multiple programs, directional microphones, manual switches). Behind-the-ear aids are typically used for patients with moderate, severe, or profound hearing loss. Despite being less cosmetically appealing than smaller units, they are more practical for elderly patients with limited vision or dexterity because they are easier to see and manipulate than other types of hearing aids.

In-the-ear hearing aids are the largest, most visible, and least expensive of the aids worn within the ear (see Figure 128-3). By definition, in-the-canal and completely-in-the-canal aids are also in the ear, but by convention, only units that occupy the full concha are referred to as in-the-ear aids. In-the-ear aids are ideal for many patients, because they do not go deep into the ear canal. They are sometimes recommended because they are larger than in-the-canal and completely-in-the-canal aids, possibly making them easier to insert and remove. In-the-ear aids are typically used for patients with mild, moderate, or, occasionally, severe hearing loss.

In-the-canal hearing aids are smaller and typically more expensive than in-the-ear aids (see Figure 128-3). In-the-canal aids are typically used for patients with mild or moderate hearing loss.

Completely-in-the-canal hearing aids are the smallest hearing aids (see Figure 128-4). A well-fitted aid in an appropriately shaped ear canal is barely visible. These aids fit so deeply into the ear canal that they require a tiny pull string to remove them. Because they are placed so close to the tympanic membrane, they require less sound pressure than traditional hearing aids to yield a similar result. The shape of these aids naturally enhances the response to high frequencies (consonants) where it is most useful, around 3000 Hz. They are often the best choice for patients with mild or moderate hearing loss.

Eyeglass hearing aids are not widely used. If the hearing aid malfunctions, patients must go without their eyeglasses. If eyeglasses are misplaced, the hearing aid is also. Frame styles for these aids are limited.

Body-worn hearing aids resemble personal stereos. The main unit, which is about the size of a deck of cards, is worn in a pocket or on a belt. The receiver is usually a custom-made clear plastic ear mold placed in the ear canal and attached to the main unit by a wire. Body-worn hearing aids are useful for patients with profound hearing loss, because they may provide 85 or 90 dB of gain, often without acoustic feedback. However, body-worn hearing aids are cosmetically unappealing. Inexpensive versions of these aids with simple headphones are often useful in patients with dementia because they can be replaced if mislaid or damaged.

Bone conduction hearing aids are excellent for patients with maximal conductive or mixed hearing loss. They may be appropriate for patients with atretic ears, hearing loss due to a hereditary syndrome, or ears for which surgical treatments are no longer possible (postoperative ears). The bone conduction hearing aid typically consists of a box (similar to the body-worn hearing aid) and wires leading to the receiver, which is a bone conduction oscillator strapped across the head. (The oscillator is much like that used for bone conduction testing.) Bone conduction hearing aids vibrate the skull, and with rare exception, there is no acoustic feedback. Therefore, these aids can overcome the conductive portion of a mixed hearing loss. However, the box and the bone oscillator are cosmetically unappealing.

Surgically implanted bone conduction hearing aids are also available. A small titanium screw is placed behind the ear in a minor procedure. After the screw integrates with the bone of the skull, an external device is attached that causes the screw to vibrate at frequencies corresponding to sounds in the patient's immediate surroundings. The vibration is heard via bone conduction. The device is approved for patients who cannot wear a conventional hearing aid (due, for example, to a wet mastoid cavity, atresia of the ear canal, or chronic otitis externa) or who have a profound hearing loss in one ear and normal hearing in the other.

Semi-implantable hearing aids are available for people with mild or moderate hearing loss. One such aid requires surgical attachment of an appliance to the chain of ossicles. An external processor attached to the scalp behind the ear causes the implanted appliance to vibrate with sound energy. Mastoidectomy, which requires general anesthesia, is required to implant the device and may deter many elderly. However, because nothing is in the ear canal, the semi-implantable devices offer 3 possible advantages: elimination of the occlusion effect associated with conventional hearing aids, avoidance of feedback, and use in patients with chronic otitis externa.

Cochlear implants: Cochlear implants are appropriate for patients with profound bilateral sensorineural hearing loss who derive little benefit from hearing aids. Accurately predicting which patient will do well with an implant is impossible. However, patients with postlingual hearing loss (ie, hearing loss that occurs after developing speech) do much better than those with prelingual hearing loss, and successful interpretation of the sounds presented by a cochlear implant is maximized when the procedure is performed as soon as possible after hearing loss occurs.

The cochlear implant is surgically placed in the inner ear, where it electrically stimulates the neural tissue of the inner ear and the 8th cranial nerve. The implant presents an auditory sensation to the patient, but the sensation is not likely to be truly speech-like. The failure rate is < 1%, and some patients have excellent results, including speech recognition while using the telephone. Nonetheless, extensive preoperative counseling regarding realistic expectations and the need for extensive aural rehabilitation is important. Patients must attend rehabilitation sessions regularly.

Assistive listening devices: Various devices can be used to make an auditory signal louder and improve the signal-to-noise ratio. Assistive listening devices are available for people with every type and degree of hearing loss. They are useful in one-on-one conversations or in movie theaters, in concert halls, at tourist attractions, and in many other venues.

Since 1991, all new telephones are required to be compatible with personal hearing aids. Hearing aids with a telecoil can be set on "T" to receive (through magnetic induction) the signal from the magnetic coil inside the telephone. While the telecoil is activated, the microphone is usually inactivated; therefore, the hearing aid does not concurrently amplify background sounds from the room in which the person is speaking.

Some behind-the-ear hearing aids have direct audio input, allowing the hearing aid to be directly coupled to the telephone (or television, radio, or other media source) with special audio boots and cords.

Many telephones have a low-high volume switch; others have replacement handsets with modular jacks, which facilitate switching between regular and amplified handsets. Portable telephone amplifiers can be easily attached and removed from the earpiece of most phones. These devices are useful for people with hearing loss who need access to more than one telephone (home, office, or cell phone) and for those who travel frequently.

Hearing aid-compatible headsets are available that use wireless technology to communicate with cellular phones and other devices. The headset can then transmit to the hearing aid with a telecoil.

Telecommunication devices for the deaf (TDDs) enable people with a hearing loss to call other TDD users and type their message using an attached keyboard. This system is similar to instant messaging on computers. The typed message is displayed on the recipient's TDD screen or printed on an optional paper scroll. Most states have a free relay service through which people with normal hearing who wish to contact a person with a hearing loss can call a relay operator who has a TDD.

Closed caption decoders are required on new televisions with screens >= 13 in. Closed captioning provides a written transcription of dialogue and sound effects for many television shows.

Infrared systems have a transmitter that sends signals from the sound source (eg, television, radio) to an infrared receiver in a headset worn by people with a hearing loss, who can adjust the loudness of the headset to their comfort level. Infrared receivers are portable and can be used in any public arena that has an infrared transmitter. However, infrared systems are ineffective in direct sunlight (some outdoor arenas), and they do not work if light transmission to the receiver is physically blocked.

FM systems have a microphone at the sound source that sends signals to a transmitter, which broadcasts the signal via FM radio waves to a receiver worn by people with a hearing loss. FM systems are portable, can be used indoors and outdoors, and can be used by people with a wide range of hearing losses. FM systems with attenuated headsets are being increasingly used by people with normal hearing and central auditory processing disorders.

Alerting systems that incorporate assistive listening devices may be used to supplement or replace auditory signals in the home and community (eg, telephone, doorbell, door knock, alarm clock, smoke and carbon monoxide detectors, home security systems, sirens, turn signal on a car). Most devices use a visual signal (eg, strobe light) or tactile signal to represent the auditory signal. For example, a device hooked up to the doorbell can set off a flashing light in the kitchen. One device can be set to flash once for a knock at the door, twice for the telephone, and one long flash followed by one short flash for the smoke detector.

Ordinary means of communication such as portable pagers and e-mail enable people with a hearing loss to easily, accurately, and instantly communicate with others.

Other strategies: Hearing dogs can help a small percentage of patients. The dogs are trained to alert patients to various auditory signals in their home, workplace, or community.

Cued speech is a system of brief hand signals used to distinguish various speech sounds that are indistinguishable through speech reading alone. For example, the sounds "p," "b," and "m" look the same on the lips. In cued speech, the speaker makes a discreet gesture at the side of the lips to identify each of the sounds.

Clear speech is simply speech that is well enunciated. Training in clear speech refocuses the speaker on pronouncing each syllable carefully and clearly but without undue exaggeration. With practice, clear speech becomes habitual, making auditory comprehension and speech reading much easier.

Aural Rehabilitation

Most patients lose their hearing gradually and are therefore unprepared for the sudden reintroduction of sounds that occurs with hearing aids. Patients may be distracted by amplification of ordinary sounds, such as the humming of a refrigerator, the turning of newspaper pages, and the sound of their footsteps on the kitchen tile. Almost all patients notice that their own voice takes on a different quality while they are wearing hearing aids.

Most patients benefit from aural rehabilitation. Typically, a small group of age-matched peers meets weekly for instruction and supervised practice in optimizing communication. Patients help set communication goals and receive instruction, hints, and insight regarding making sense of sounds they have not heard for a long time. Time and patience are required, but working with professionals who are experts in maximizing communication makes the process easier and less frustrating.

Sessions almost always include training in speech reading (lip reading). Patients are taught which sounds are visible on the lips, teeth, and tongue and which are not. The need to notice facial expressions and gestures is stressed, and patients are reminded that context, linguistic redundancy, and familiarity with common English idioms contribute to the understanding of conversations, even when patients cannot hear every word.

Training includes teaching patients to become advocates for their own needs. Learning to anticipate difficult communication situations and to modify or avoid them gives the patient a sense of control over the listening environment. For example, patients can visit a restaurant during off-peak hours, when it is quieter. They can ask for a booth, which blocks out some extraneous sounds. They can request that specials of the day be written rather than spoken. At the beginning of a telephone conversation, identifying themselves as hearing-impaired may make obtaining information over the telephone easier. In direct conversations, asking the speaker to face them can help greatly.

This topic was last updated December 2005.