Presbycusis or age-related hearing loss.
It is the cumulative effect of aging on hearing.
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.
Presbycusis hearing loss is most marked at higher frequencies.
Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis.
Differentiating the individual effects of distinct causes of hearing loss can be difficult.
The cause of presbycusis is a combination of genetics, cumulative environmental exposures and pathophysiological changes related to aging.
At present there are no preventive measures.
Treatment is by hearing aid or surgical implant.
Presbycusis is the most common cause of hearing loss, affecting one out of three persons by age 65, and one out of two by age 75.
Presbycusis is the second most common illness next to arthritis in aged people.
Many vertebrates such do not experience presbycusis in old age as they are able to regenerate their cochlear sensory cells, whereas mammals including humans have genetically lost this regenerative ability.
Teenagers begin to lose the ability to hear high-pitched sounds.
Primary symptoms:
sounds or speech becoming dull, muffled or attenuated
A 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
Secondary symptoms:
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
Presbycusis occurs after age 50, but deterioration in hearing has been found to start very early, from about the age of 18 years.
Age affects high frequencies more than low, and men more than women.
Age-related hearing loss may only become noticeable later in life.
The effects of age can be exacerbated by exposure to environmental noise, exposure to ototoxic drugs and chemicals.
Noise-induced hearing loss (NIHL) and is distinct from presbycusis.
With presbycusis, over time, the detection of high-pitched sounds becomes more difficult, and speech perception is affected, particularly of sibilants and fricatives.
Patients typically express a decreased ability to understand speech.
Once the loss has progressed to the 2–4 kHz range, there is increased difficulty understanding consonants.
Both ears tend to be affected with presbycusis.
Adults with presbycusis often exhibit associated symptoms of social isolation, depression, anxiety, frailty and cognitive decline.
The risk of having cognitive impairment with presbycusis increases 7 percent for every 10 dB of hearing loss at baseline.
The hearing aging process has three distinct components: physiologic degeneration, extrinsic damage (nosocusis), and intrinsic damage (sociocusis).
These factors are superimposed on a genetic substrate, and may be overshadowed by general age-related susceptibility to diseases and disorders.
Hearing loss is only weakly correlated with age, as in preindustrial and non-industrial societies, persons retain their hearing into old age.
In the Framingham cohort study, only 10% of the variability of hearing with age could be explained by age-related physiologic deterioration.
Within family groups, heredity factors are dominant.
Across family groups, other, presumably sociocusis and nosocusis factors were dominant in hearing loss.
Heredity: factors like early aging of the cochlea and susceptibility of the cochlea for drug insults are genetically determined.
Sociocusis is the condition of hearing loss attributed to continuous noise exposures, unrelated to job or occupation: noises from traffic, home appliances, music, television, and radio.
The accumulated exposure to these noises over many years can lead to a condition similar to pure presbycusis.
Nosocusis factors are those that can cause hearing loss, which are not noise-based and separate from pure presbycusis, include:
Ototoxic drugs: Ingestion of ototoxic drugs like aspirin may hasten the process of presbycusis.
vascular degeneration
Atherosclerosis: May diminish vascularity of the cochlea, thereby reducing its oxygen supply.
Dietary habits: Increased intake of saturated fat may accelerate atherosclerotic changes in old age
Smoking: Is postulated to accentuate atherosclerotic changes in blood vessels aggravating presbycusis.
Diabetes: May cause vasculitis and endothelial proliferation in the blood vessels of the cochlea, thereby reducing its blood supply.
Hypertension: causes potent vascular changes, like reduction in blood supply to the cochlea, thereby aggravating presbycusis.
A recent study found that diabetes, atherosclerosis and hypertension had no correlation to presbycusis, suggesting that these are nosocusis factors, not intrinsic factors.
There are four pathological phenotypes of presbycusis:
Sensory: characterized by degeneration of the organ of Corti, the sensory organ for hearing.
The organ of Corti, located within the scala media, it contains inner and outer hair cells with stereocilia.
The outer hair cells play a significant role in the amplification of sound.
Age-related hair cell degeneration is characterized by loss of stereocilia, shrinkage of hair cell soma, and reduction in outer hair cell mechanical properties.
That suggests that functional decline in mechanotransduction and cochlear amplification precedes hair cell loss and contributes to age-related hearing loss.
Hair cell aging is associated with key molecular processes of transcriptional regulation, DNA damage/repair, autophagy, and inflammatory response,.
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.
These pumps 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.
Conductive: due to stiffening of the basilar membrane thus affecting its movement: not been verified as contributing to presbycusis.
The audiogram can categorize abrupt high-frequency loss as sensory phenotype or flat loss as strial phenotype.
The mainstay of SNHL is strial, with only about 5% of cases being sensory.
This type of presbycusis is manifested by a low-frequency hearing loss, with unimpaired speech recognition.
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, making amplification difficult due to poor comprehension.
A sensory presbycusis audiogram shows 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.
Hearing loss is classified as mild, moderate, severe or profound.
Audiometry for air conduction thresholds at 250, 500, 1000, 2000, 4000, 6000 and 8000 Hz is traditionally used to classify the degree of hearing loss in each ear.
Normal hearing thresholds are considered to be 25 dB sensitivity, but 15 dB is more typical.
Mild hearing loss is thresholds of 25–45 dB; moderate hearing loss is thresholds of 45–65 dB; severe hearing loss is thresholds of 65–85 dB; and profound hearing loss thresholds are greater than 85 dB.
Otoscopy allows some inspection of the middle ear through the translucent tympanic membrane.
Tympanometry is a test of the tympanic membrane and middle ear function using a tympanometer, an air-pressure/sound wave instrument inserted into the ear canal.
A tympanogram shows 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.
Audiometry: 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, showing a significant hearing loss without an air-bone gap that is characteristic of conductive hearing disturbances.
Sensorineural pattern hearing loss: air conduction is equal to bone conduction.
Persons with cochlear deficits fail otoacoustic emissions testing.
People pwith 8th cranial nerve (vestibulocochlear nerve) deficits fail auditory brainstem response testing.
MRI and other types of scan cannot directly detect or measure age-related hearing loss.
Treatment:
At present, presbycusis, is primarily sensorineural in nature, and cannot be prevented, ameliorated or cured.
Treatment options for presbycusis fall into 2 categories: surgical and management.
There are no approved or recommended pharmaceutical treatments for presbycusis.
In cases of severe or profound hearing loss, a surgical cochlear implant is possible.
A cochlear implant is an electronic device that replaces the cochlea of the inner ear.
Electrodes are typically inserted through the round window of the cochlea, into the fluid-filled scala tympani.
They stimulate the peripheral axons of the primary auditory neurons, which then send information to the brain via the auditory nerve.
The cochlea is tonotopically mapped in a spiral fashion, with lower frequencies localizing at the apex of the cochlea, and high frequencies at the base of the cochlea, near the oval and round windows.
Aging results in a loss in distinction of frequencies, especially higher ones.
The electrodes of the implant are designed to stimulate the array of nerve fibers that previously responded to different frequencies accurately.
Due to spatial constraints, the cochlear implant may not be inserted all the way into the cochlear apex.
It provides a different kind of sound spectrum than natural hearing, but may enable the recipient to recognize speech and environmental sounds.
Middle ear implants are surgically implanted hearing aids inserted onto the middle ear.
These aids work by directly vibrating the ossicles, and are cosmetically favorable due to their hidden nature.
Hearing aids can now be tuned to specific frequency ranges of hearing loss.
Techniques such as squarely facing the affected person, enunciating, ensuring adequate light, minimizing noise in the environment, and using contextual cues are used to improve comprehension.
Water-soluble formulation of coenzyme Q10 (CoQ10) causes a significant improvement in liminar tonal audiometry of the air and bone thresholds at 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz.