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LESSON 139

Presbycusis

Year 2
Spring semester
Disorders of the Auditory and Vestibular Systems
Inner ear and retrocochlear disorders
Duration: 11:06

We explain age-related hearing loss (presbycusis) through the Schuknecht types, the typical audiogram and the warning signs. We also cover how high-frequency loss affects speech understanding, and how hearing loss relates to communication and cognitive health.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will learn about age-related hearing loss, or presbycusis.
We will cover the Schuknecht types, the typical audiogram, and the effects of hearing loss on communication and cognitive health.
Presbycusis, or age-related hearing loss, abbreviated ARHL, is a sensorineural loss that comes with ageing.
It usually develops in both ears together and in a similar way, that is, symmetrically.
The loss begins at the high frequencies and over time spreads toward lower frequencies.
There is no fixed age of onset, but changes often become noticeable in a person's fifties and sixties.
Because it progresses slowly, people often do not notice their loss for a long time; those around them notice it first.
There is no single cause; along with ageing, genetic susceptibility, noise history and general health all play a part.
Age-related hearing loss is one of the most common sensory problems in adults, and its prevalence rises sharply with age.
According to the World Health Organization, more than a quarter of people over sixty have disabling hearing loss.
As the population ages, this number is expected to rise further in the coming decades.
It tends to appear somewhat earlier and more markedly in men; differences in noise exposure also play a part.
Noise, smoking, diabetes and cardiovascular disease have been linked with earlier and faster development of the loss.
If we imagine the cochlea unrolled, the apex responds to low-pitched sounds and the base to high-pitched sounds.
Age-related changes usually affect the hair cells at the base of the cochlea first.
One explanation: the wave passes the base at every frequency; basal cells are also metabolically loaded and prone to oxidative damage.
So on the audiogram, the first change is usually seen in the region from four thousand to eight thousand hertz.
As the loss progresses to two thousand hertz and below, speech understanding also begins to be affected.
Based on studies of human temporal bones, Harold Schuknecht classified presbycusis into four main types.
In the sensory type, hair cells at the base of the cochlea are lost, and the audiogram shows an abrupt high-frequency drop.
In the neural type, spiral ganglion neurons decrease; speech discrimination is disproportionately poor for the audiogram.
In the metabolic, or strial, type the stria vascularis weakens; the audiogram is flat or gently sloping and discrimination is usually good.
In the mechanical type, the basilar membrane is thought to stiffen, and the audiogram slopes down smoothly toward the high frequencies.
Schuknecht later added mixed and indeterminate types, because many people did not fit a single type.
The stria vascularis is a tissue rich in blood vessels on the lateral wall of the cochlear duct.
Its role is to regulate the endolymph in the scala media and to create the endocochlear potential of about plus eighty millivolts.
This potential acts like a battery for the hair cells; when it drops, cochlear amplification weakens over a wide frequency range.
Animal studies have shown that strial changes play an important role in ageing.
So in the metabolic type, the loss affects many frequencies together rather than one region, giving a flat audiogram.
Today it is accepted that pure types are rare and that most people have several mechanisms at once.
It is often impossible to separate the effect of ageing from noise damage accumulated over a lifetime.
Animal studies have shown that synapses between inner hair cells and nerve fibers can be lost before the hair cells are.
Age-related changes in the brainstem and cortex also affect understanding in noise and temporal processing in particular.
So even if two people have similar audiograms, their difficulties in daily life can be very different.
In this example, the low frequencies of the right ear are within normal limits; above two thousand hertz the thresholds worsen steadily.
The left ear looks almost the same, so the loss is bilateral and symmetric.
Bone conduction thresholds overlap air conduction; there is no air-bone gap, and the loss is sensorineural.
This downward slope toward the high frequencies is the most typical picture of age-related hearing loss.
The person hears sounds in quiet, but may struggle to understand speech clearly because high-pitched consonants are missed.
Not every hearing loss in an older person is presbycusis.
A bilateral, symmetric, slowly progressing loss with no air-bone gap is consistent with age-related loss.
In contrast, a clear asymmetry between the ears may require further assessment for retrocochlear causes.
Sudden or rapid worsening, one-sided tinnitus or dizziness are also findings that call for referral to a physician.
If there is an air-bone gap, an outer or middle ear problem should be considered in addition to age.
So presbycusis is a diagnosis of exclusion; other causes are ruled out by a physician's assessment.
A clinical tip: in older adults, always do otoscopy before starting the test.
Impacted earwax is common in this age group and can make thresholds look worse than they are.
Also, an ear canal whose elasticity has changed with age can collapse under the pressure of supra-aural earphones.
Canal collapse can create a false air-bone gap, especially at high frequencies; if in doubt, repeat the test with insert earphones.
With high-frequency loss, consonants such as s, sh, f, th, t and k are the parts of speech most easily lost.
Vowels, whose energy is mostly at low frequencies, are still heard, so the person hears speech but cannot make out the words clearly.
This is why the complaint "I can hear, but I cannot understand" is so typical of presbycusis.
The difficulty increases clearly in noisy places and when several people are talking.
Following fast speech also becomes harder, because temporal processing slows with age.
Constantly listening hard, that is, increased listening effort, leads to marked fatigue by the end of the day.
Assessment begins with pure tone audiometry and speech audiometry.
If possible, a speech-in-noise test is also done, because it reflects daily difficulty better than testing in quiet.
The person's own complaints and the family's observations are recorded, along with standard questionnaires.
Where the person struggles and what they want to achieve form the basis of the rehabilitation plan.
If cognitive screening is planned, remember that hearing loss can lower performance on verbal tests.
The audiologist turns this information, together with the physician's assessment, into a holistic plan.
As communication gets harder, a person may withdraw from crowded places and social activities, which increases loneliness.
Many studies have shown a link between age-related hearing loss and depressive symptoms.
The Lancet Commission on dementia counted midlife hearing loss among the main modifiable risk factors for dementia.
Possible explanations include the brain's adaptation to reduced auditory input, increased listening load, and social isolation.
In a large randomized trial, hearing intervention did not significantly slow cognitive decline across all participants.
But decline appeared to slow in a higher-risk subgroup; this finding needs to be confirmed by new studies.
So it is not yet fully known to what extent the link between hearing loss and dementia is one of cause and effect.
Regular hearing screening in adults allows hearing loss to be noticed early.
For suitable people, hearing aids are one of the main options for supporting hearing.
Yet many people wait for years before seeking help, and hearing aid use rates remain low.
Strategies such as talking face to face, reducing background noise and asking for repetition make communication easier.
Involving family members improves both adjustment and the benefit in daily life.
The right approach for each person is decided together after audiological and medical assessment.
Presbycusis is usually a bilateral, symmetric sensorineural loss that slopes toward the high frequencies.
Schuknecht described four basic types: sensory, neural, metabolic and mechanical.
Asymmetry, sudden or rapid worsening, and an air-bone gap suggest other causes.
Hearing loss can affect communication, social life and cognitive health.
Test yourself: in the Schuknecht classification, which type is caused by atrophy of the stria vascularis?
The correct answer is C: the metabolic, or strial, type.
Because the endocochlear potential drops, the audiogram is usually flat or gently sloping.
In the next lesson we will look at noise-induced hearing loss and the four thousand hertz notch on the audiogram.
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Prerequisites

LESSON 63 Audiogram Configurations and What They Suggest

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