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Professor Frank R. Lin, professor of otolaryngology and surgery and director of the Cochlear Hearing Center at the Johns Hopkins School of Medicine, has authored an advanced scientific review on age-related hearing loss.

A scientific study of hearing loss

As published in the April 24 issue of the New England Journal of Medicine (N Engl J Med), Professor Lin began his presentation by saying: “Age-related hearing loss gradually affects each person over the course of their lifetime. ”. A person’s ability to hear depends on the “work efficiency” of the cochlea in the inner ear, which accurately encodes sounds, converts them into neural signals, and then transmits them to the brain. In the cerebral cortex, these neural signals are processed and coded, transforming the words a person hears into something that can be understood.

Pathological processes occurring at any level of this pathway from the ear to the brain can negatively affect hearing. But the most common cause is age-related hearing loss involving the cochlea.

A presentation of the latest and most advanced review on age-related hearing loss covers the following points:

1- Age-related hearing loss is characterized by a “gradual” decline in the efficiency of sensory hair cells in the inner ear, resulting in the death of many of them. These are specialized cells primarily responsible for encoding sound and converting it into nerve signals. One of the most important properties of these cells – unlike other cells throughout the body – is that they cannot renew themselves.

Due to the cumulative effects of multiple processes and their damaging influences, these cells gradually decrease in number throughout life. A strong risk factor for age-related hearing loss is aging. Lighter skin color, an indicator of the amount of cochlear pigmentation – because melanin protects the cochlea – male gender and exposure to noise are other important factors.

There are other risk factors that are not being addressed, such as heart disease, diabetes, smoking, and high blood pressure. All of these may contribute to microvascular injury in the cochlea of ​​the inner ear.

Hearing loss

2- Beginning in adulthood, hearing acuity begins to decline gradually; Especially regarding high frequency sounds. The prevalence of clinically significant hearing loss increases throughout life.

To illustrate, the extent of a person’s hearing loss roughly doubles with each decade of life, with more than two-thirds of adults 60 or older experiencing clinically significant hearing loss. Statistics indicate that in the United States in 2019, nearly 73 million people, or one in five, were estimated to suffer from hearing loss. Epidemiological studies, on the one hand, show a link between hearing loss and poor communication skills, cognitive impairment, dementia, higher medical costs and other harmful health outcomes.

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Clinical research over the past decade has focused particularly on understanding the effects of hearing loss on cognitive decline and dementia. Based on accumulated scientific evidence, the Lancet Commission on Dementia concluded that hearing loss in middle age and beyond is the largest modifiable risk factor for dementia, representing 8 percent of all cases of dementia in 2020.

Key mechanisms hypothesized to increase the risk of hearing loss, cognitive decline, and dementia include impaired auditory encoding of sound and the deleterious effects of hearing loss on cognitive impairment, brain degeneration, and social isolation.

3- Age-related hearing loss in both ears appears gradually over time, subtle and obvious, without an identifiable causative event being noticed. It affects how strongly voices are heard, how clearly they are articulated, and a person’s daily communication skills. People with mild hearing loss often don’t realize they have a hearing loss. Instead, they believe that their hearing loss is caused by external factors (for example: others not speaking clearly or background noise).

But with more severe hearing loss, people may often notice problems with speech intelligibility, even in quiet environments. Conversations in noisy environments are actually stressful for them, possibly because of the increased mental effort their brains have to expend processing ambiguous speech signals and their cochlea malfunctioning. Often, a person’s family members are very aware of the person’s hearing loss.

Assessment of listening problems

4- To assess a patient’s hearing problems, it is important to understand that a person’s sense of hearing depends on 5 components:

– Incoming sound quality. For example; Because the speech signal is distorted in rooms and halls with background noise or reverberant acoustics.

– Mechanical conduction of sound through the outer ear, then the middle ear, to the cochlea (i.e., conductive hearing).

-Transmits the sound signal as a neural signal through the cochlea.

– Transmitting these nerve signals to the brain (i.e., sensorineural hearing).

– Interpretation of the neural signal by the cerebral cortex (i.e., central auditory processing).

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When a patient notices hearing problems, the cause may be any of these components. In many cases, more than one of these factors causes hearing loss before a person has hearing problems.

5- The goal of the initial clinical evaluation is to evaluate the patient for forms of conductive hearing loss; Because it is easily treatable, look for other forms of hearing loss that require further evaluation by a specialist ear, nose and throat doctor. Transmissive forms of hearing loss that are easily treated by a primary care physician—that is, do not require a specialist in ear, nose, and throat diseases—include otitis media and cerumen impaction (auditory). These can be diagnosed based on clinical history (for example, acute onset with otalgia and ear fullness with an upper respiratory tract infection) or by otoscopy looking for a thorough impaction of cerumen in the ear canal.

On the other hand, signs and symptoms associated with hearing loss that require further evaluation or consultation with an otolaryngologist include fluid drainage from the ear, or an abnormal endoscopic examination, persistent ringing in the ears (intermittent tinnitus) or vertigo, or variable or asymmetric hearing, or sudden hearing loss without evidence of a conductive cause (e. .g., moderate hearing loss due to otitis media). Technological changes now allow adults to self-examine, monitor their hearing using a smartphone (, and purchase hearing aids without a prescription. This approach is consistent with broader trends toward empowering consumers with the knowledge and options to act on their health without a medical intermediary.

6- Sudden sensorineural hearing loss (SSNHL) is one of the few forms of hearing loss that requires urgent evaluation by an otolaryngologist (ideally within 3 days of onset). This is because early diagnosis and therapeutic intervention with a cortisone derivative may improve the chances of hearing recovery. Sudden sensorineural hearing loss is a relatively rare event; Its annual incidence is 1 in 10,000 people, and it usually occurs in people aged 40 years or older. Compared to unilateral hearing loss due to conduction, patients with sudden sensorineural hearing loss have severe, painless hearing loss in one ear, resulting in an inability to hear or understand speech in the affected ear.

Treatment of hearing loss

7- Currently, there are no rehabilitative therapies with maximal efficacy for age-related hearing loss. “Rehabilitation therapy” refers to achieving maximum functional efficiency of a medically diseased organ, enabling the patient to maintain independence after the effects of disease or injury. This is completely different from rehabilitation therapy.

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Therefore, the management of age-related hearing loss currently focuses on three aspects: the first is to preserve hearing and strengthen communication. “Hearing protection strategies” focus on reducing exposure to noise by moving away from the sound source or reducing the volume and using hearing protection devices (such as earplugs) when necessary.

“Strategies to strengthen communication” include encouraging people to talk face-to-face, to keep a distance when speaking, and to reduce background noise. Face-to-face communication allows the ear to receive a clearer audio signal. Face-to-face communication allows the listener visual access to facial expressions and lip movements that may aid central decoding of the speech signal.

Age-related hearing loss is associated with a “gradual” decline in the efficiency of sensory hair cells

8- A second area of ​​focus in the treatment of age-related hearing loss is to adopt strategies to improve the quality of the incoming audio signal (ie, to overcome the effects of competing background noise on hearing clearly and understanding speech sounds).

A third aspect is the use of specific hearing technologies such as hearing aids (hearing aids) and cochlear implants. The goal is to increase the clarity of the speech signal and the person’s understanding of its meanings and interactions with it.

Evidence from clinical studies shows that hearing aid use improves communication and quality of life, and can slow the decline and loss of cognitive abilities within 3 years in older adults at risk of cognitive impairment and dementia.

9- Among people who could benefit from hearing aid use or cochlear implant use (as determined by their hearing test results) there is much less. Among people with hearing loss in the United States, hearing aid use is less than 20 percent, and cochlear implantation prevalence is less than 5 percent.

The reasons for the low reliability of these treatment strategies are indeed multifactorial. These include factors such as: stigma (perception that fitting a hearing aid is a shame), poor access to and inability to afford hearing intervention treatments, and the inability of hearing technologies to fully compensate for age-related deterioration of peripheral encoding of sound. – related hearing loss.

* Consultant in Internal Medicine

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