Presbycusis – Causes, Symptoms, Diagnosis, Treatment

Presbycusis refers to bilateral age-related hearing loss. In literal terms, presbycusis means “old hearing” or “elder hearing.” It becomes noticeable around age 60 and progresses slowly; however, there is evidence that certain stressors can speed the rate of deterioration. The diagnosis can be confirmed with audiometry. The hallmark of presbycusis is the impaired ability to understand high-frequency components of speech (voiceless consonants, such as p, k, f, s, and ch). There is no cure; however, hearing aids that amplify sounds can be used to mitigate symptoms. Anatomically, presbycusis involves multiple components of the auditory system. It is primarily due to age-related changes in hair cells, the stria vascularis, and afferent spiral ganglion neurons.

Presbycusis (also spelled presbyacusis, from Greek press “old” + akousis hearing), or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging (nosocusis and sociocusis) is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.

During the normal hearing, sound, in the form of air vibration, is captured by the funnel-shaped external ear and is directed to the tympanic membrane. This causes the tympanic membrane to vibrate at a specific frequency and amplitude. This movement is amplified by three small bones in the middle ear: the malleus, incus, and stapes. From there, the signal proceeds as vibrations that are transmitted through the fluid within the inner ear to the cochlea. In the cochlea, receptors known as hair cells transform the information encoded in the vibrations into a neurologic signal which travels to the auditory cortex via the cochlear nerve.

Pathophysiology

Examples of microscopic changes seen in this condition are hair cell degeneration of the cochlea and giant stereociliary degeneration.

There are four pathological phenotypes of presbycusis:

  • Sensory – characterized by degeneration of the organ of Corti, the sensory organ for hearing. Located within the scala media, it contains hair cells with stereocilia, which extend to the tectorial membrane. The organ’s outer hair cells play a significant role in the amplification of sound and is extremely sensitive to external and internal factors. If the outer hair cells are damaged, they do not regenerate. This results in a loss of sensitivity of hearing, as well as an abnormal perceived loudness in the aspect of the tonotopic spectrum that the damaged cells serve.
  • Neural – characterized by degeneration of cells of the spiral ganglion.
  • Strial/metabolic – characterized by atrophy of stria vascularis in all turns of cochlea. Located in the lateral wall of the cochlea, the stria vascularis contains sodium-potassium-ATPase pumps that are responsible for producing the endolymph resting potential. As individuals age, a loss of capillaries leads to the endolymphatic potential becoming harder to maintain, which brings a decrease in cochlear potential.
  • Cochlear conductive – due to stiffening of the basilar membrane thus affecting its movement. This type of pathology has not been verified as contributing to presbycusis.

In addition, there are two other types:

  • Mixed
  • Indeterminate

The shape of the audiogram categorizes abrupt high-frequency loss (sensory phenotype) or flat loss (strial phenotype).

The mainstay of SNHL is trial, with only about 5% of cases being sensory. This type of presbycusis is manifested by a low-frequency hearing loss, with unimpaired speech recognition.

Classically, audiograms in neural presbycusis show a moderate downward slope into higher frequencies with a gradual worsening over time. A severe loss in speech discrimination is often described, out of proportion to the threshold loss, making amplification difficult due to poor comprehension.

The audiogram associated with sensory presbycusis is thought to show a sharply sloping high-frequency loss extending beyond the speech frequency range, and clinical evaluation reveals a slow, symmetric, and bilateral progression of hearing loss.

Causes of Presbycusis

Presbycusis is multifactorial in origin. In addition to age-related degeneration leading to physiologic and anatomic changes, other contributing factors include genetic factors, hormones, exposure to loud noises or ototoxic agents, history of ear infection, and the presence of certain systemic diseases.

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Age-related Factors

Presbycusis can be broken down further with regards to which structures and functions are primarily affected. Some argue that there is little clinical utility in subdividing presbycusis as there is no significant change in approach or treatment, and oftentimes mixed pathology is present. Presently, there are thought to be six categories of presbycusis: sensory, neural, trial, mechanical, mixed, and indeterminate.

  • Sensory presbycusis – loss of receptor hair cells at the basal aspect of the cochlea resulting in characteristic high-frequency hearing loss.
  • Neural presbycusis – loss of cochlear nerve fibers as well as the loss of spiral ganglion neurons.
  • Strial presbycusis – degeneration of stria vascular cells. These cells are essential for maintaining the appropriate ion composition of endolymph to generate the endocochlear potential for signal transduction. Sometimes referred to as metabolic presbycusis.
  • Mechanical presbycusis (cochlear conductive) – due to physical changes of the cochlear duct. This is accompanied by a specific audiogram pattern.
  • Mixed presbycusis – characterized by pathologic changes in more than one of the above structures
  • Indeterminate presbycusis – cases in which changes to the above structures are not significant.
  • Genetic Factors – Genetic factors, specifically, differences in mitochondrial DNA expression genes related to oxidative stress, have been found in patients with presbycusis when compared to controls.
  • Ototoxic Factors – There are multiple medications associated with ototoxicity, including salicylates, loop diuretics, aminoglycoside, and certain chemotherapeutic agents. Additionally, some work and environmental-related exposures to chemicals such as toluene, styrene, lead, carbon monoxide, mercury, and other toxins have been shown to cause ototoxicity. Minimizing exposure to these agents can help to prevent age-related hearing loss.
  • Noise Exposure Factors – Some long-term studies have shown that individuals who have sustained noise-induced cochlear damage in their youth go on to develop more severe presbycusis. Anatomically, noise exposure may lead to damage and subsequent loss of spiral ganglion neurons.
  • Hormonal Factors – Glucocorticoids, sex hormones, and glutamate signaling are thought to play a role in presbycusis. Prolonged corticosterone levels and loss of nuclear factor kappa B have been associated with increased spiral ganglion neuron loss. The use of progestin and combination hormone replacement therapy in postmenopausal is associated with a more frequent incidence of hearing loss.

Symptoms of Presbycusis

Primary symptoms:

  • sounds or speech becoming dull, muffled or attenuated
  • need for increased volume on television, radio, music and other audio sources
  • difficulty using the telephone
  • loss of directionality of sound
  • difficulty understanding speech, especially women and children
  • difficulty in speech discrimination against background noise (cocktail party effect)
  • hyperacusis, heightened sensitivity to certain volumes and frequencies of sound, resulting from “recruitment”
  • tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present

Diagnosis of Presbycusis

Presbycusis is generally insidious in onset, and mild cases are difficult to detect. It is imperative that primary care physicians screen for hearing loss, especially geriatricians and those caring for adults age 60 and beyond. Screening for hearing impairment is part of the ‘Welcome to Medicare Visit.” Often, family members and friends are more aware of hearing loss than patients themselves. A common initial presentation is a difficulty discriminating speech in specific situations, such as a room with significant background noise. Some patients complain of tinnitus, or ringing in the ears, however, this is not specific to presbycusis. Formal questionnaires exist, such as the Hearing Handicap Inventory for the Elderly-Screening (HHIE-S). However, some investigators found this formal screening tool to be less sensitive and more time-consuming than the single question “Do you have a hearing problem now?” Gathering a thorough history regarding the patient’s ability to communicate, and ideally getting input from a close contact can help to identify individuals who should be sent for further audiometry testing. Asking about recreational or occupational exposure to loud noises, the use of ototoxic medications, and family history of age-related hearing loss is also important. Referral to an otolaryngologist should be considered if the patient’s hearing loss is acute, unilateral, or accompanied by neurologic symptoms, such as facial numbness or weakness, loss of balance, or dizziness.

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The general physical exam is usually unremarkable in patients with presbycusis. It is common for older adults to have age-related benign opacification of the tympanic membrane and build-up of cerumen. If a moderate amount of cerumen is present, this should be removed to rule out impaction or obstruction as a potential cause of hearing loss. Tuning forks may be used to discriminate between conductive and sensorineural hearing loss; however, their use is limited by patient cooperation and physician subjectivity. Determining whether the pattern of hearing loss is sensorineural or conductive is an important first step in the diagnosis. This can be done by performing both Weber’s test and the Rinne test using a tuning fork. These tests should not be used as screening or diagnostic tools, but simply for differentiating between conductive and sensorineural hearing loss. Presbycusis is sensorineural in origin; therefore, the Rinne test should reveal that air conduction is heard longer than bone conduction in both ears. Weber’s test should localize toward the ear with better hearing, signifying a contralateral sensorineural loss. Weber’s test may vary and may result in a falsely normal result if hearing loss is symmetric.

Evaluation

Routine physical exam maneuvers alone are not sufficient for diagnosing presbycusis. An in-office screening audiometry test administered by trained personnel should be considered by providers such as geriatricians who have a large population of older adults at high risk of presbycusis. There should be a low threshold for referral for definitive auditory testing in patients suspected of presbycusis. Imaging is usually not performed except in cases in which there is a discrepancy between presentation and auditory testing, or there are associated neurological changes.

There are many variations of audiometry testing and central auditory testing that are beyond the scope of this review. In general, an audiometry exam tests the ability to hear sounds at varying intensity (loudness) and frequencies (tone). Commonly, pure tone testing (also known as an audiogram) is performed in patients with suspected age-related hearing loss. Pure tones are delivered through the use of headphones to one ear at a time. Patients are asked to respond if they hear a sound. The results are presented in the form of an audiogram, a graph with hearing level (in decibels) on the y-axis and frequency (in hertz) on the x-axis. In presbycusis, the highest frequency sounds are typically affected first, followed by lower and lower frequency sounds as the condition progresses. Presbycusis is characterized by bilateral hearing loss above 2000 Hz. On a standard audiogram, presbycusis appears as an overall down-sloping line that represents impaired hearing at higher frequency sounds.

  • Laboratory testing – for diseases commonly associated with hearing loss, such as dyslipidemia, diabetes, and renal dysfunction, may be indicated but are not required for diagnosis.Tinnitus occurring in only one ear should prompt the clinician to initiate further evaluation for other etiologies. In addition, the presence of a pulse-synchronous rushing sound may require additional imaging to exclude vascular disorders.
  • Otoscopy – An examination of the external ear canal and tympanic membrane performed by a medical doctor, otolaryngologist, or audiologist using an otoscope, a visual instrument inserted into the ear. This also allows some inspection of the middle ear through the translucent tympanic membrane.
  • Tympanometry – A test administered by a medical doctor, otolaryngologist or audiologist of the tympanic membrane and middle ear function using a tympanometer, an air-pressure/sound wave instrument inserted into the ear canal. The result is a tympanogram showing ear canal volume, middle ear pressure and eardrum compliance. Normal middle ear function (Type A tympanogram) with a hearing loss may suggest presbycusis. Type B and Type C tympanograms indicate an abnormality inside the ear and therefore may have an additional effect on the hearing.
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Laboratory studies

This may include a blood or other sera test for inflammatory markers such as those for autoinflammatory diseases.

  • Audiometry – A hearing test administered by a medical doctor, an otolaryngologist (ENT) or audiologist including pure tone audiometry and speech recognition may be used to determine the extent and nature of hearing loss, and distinguish presbycusis from other kinds of hearing loss. Otoacoustic emissions and evoked response testing may be used to test for audio neuropathy. The diagnosis of a sensorineural pattern hearing loss is made through audiometry, which shows a significant hearing loss without the “air-bone gap” that is characteristic of conductive hearing disturbances. In other words, air conduction is equal to bone conduction. Persons with cochlear deficits fail otoacoustic emissions testing, while persons with 8th cranial nerve (vestibulocochlear nerve) deficits fail auditory brainstem response testing.
  • Magnetic resonance imaging (MRI) – As part of differential diagnosis, an MRI scan may be done to check for vascular anomalies, tumors, and structural problems like enlarged mastoids. MRI and other types of scan cannot directly detect or measure age-related hearing loss.

Treatment of Presbycusis

There is no cure for presbycusis. Hearing aids are the mainstay of treatment and have been shown to have a significantly positive effect on the quality of life and communication. Hearing aids do have limitations. They do not repair normal hearing, but instead simply amplify sounds. Devices can be very expensive and often are not covered by the patient’s insurance. While smaller hearing aids are potentially more comfortable and discrete, decreased dexterity in geriatric patients may make these devices less convenient. Importantly, the management of hearing aids does not stop once the devices are fitted. Learning to use hearing aids and adjusting to both the physical discomfort and cognitive adjustment takes significant effort and practice. A collaborative, interdisciplinary approach involving the primary care provider and audiologist is recommended for continued auditory rehabilitation. Patients often require encouragement as many find hearing aids uncomfortable, unattractive, and embarrassing. Hearing aids are indicated at certain thresholds of hearing loss. Cochlear implants can be offered to patients with severe bilateral hearing loss that is not improved with hearing aids. Specific criteria exist for patients to be considered candidates, and often include a predetermined level of impairment in word identification.

As extrinsic factors are thought to have a role in the progression of presbycusis, wearing earplugs or earmuffs to attenuate sounds may be helpful if the patient needs to be exposed to loud noises. A diet low in saturated fat may help slow hearing loss. Maintaining a healthy, active lifestyle is a logical form of risk reduction in light of the fact that hearing loss is associated with stroke, myocardial ischemia, hypertension, hyperlipidemia, and diabetes. Smoking should be discouraged, as cessation has been shown to delay age-related hearing loss.

There is an abundance of ongoing research regarding the genetic and metabolic components of age-related hearing loss. Due to the potential role of oxidative damage, it was thought that antioxidants might slow the progression of hearing loss. While the administration of alpha-lipoic acid has been shown to prevent age-related hearing loss in rats, an antioxidant-enriched diet in humans did not delay the progression of hearing loss. Other agents, such as coenzyme Q-10 and Ginko biloba, have been studied and lack sufficient evidence for use. Additionally, the use of these supplements is controversial as prolonged administration has been associated with an increase in overall mortality. There are ongoing investigations into potential gene and hormone therapies for hearing loss.

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