Sensorineural Hearing Loss And Aging

Introduction

Definition of sensorineural hearing loss and ageing

Sensorineural hearing loss or deafness, also known as presbycusis, occurs due to damage within the structures of the inner ear. The innerr ear serves as a point of origin for the auditory nerve, which carries sound signals from the inner ear to the brain. Gradual hearing loss is the natural process that occurs with age and is infuenced by various factors.. Sensorineural hearing loss is caused by a combination of factors such as genetics, environmental exposures and age-related physiological changes. 

Ageing is a natural process that affects all aspects of our body, including our hearing. As we age, our bodies undergo changes that can lead to degeneration of the hair cells in the inner ear and the associated neural pathways. This degeneration can consequently result in sensorineural hearing loss, which can be further exacerbated by  factors like noise exposure and genetics. Age-related sensorineural hearing loss typically starts with high-frequency sounds and progresses gradually over time.

Importance of the topic

Ageing is one of the most common causes of sensorineural hearing loss, and it is estimated that around one-third of people over 65 years old experience somedegree of this type of hearing impairment. Age-related sensorineural hearing loss accounts for 90% of all hearing loss cases.¹

Purpose of the outline

Causes of sensorineural hearing loss and aging

Age related changes in the ear

Age induces changes in the ear which affects the hearing ability. These age-related changes are complex and involve alteration of the nerve pathways that are originating in the inner ear. The inner ear consists of the cochlea and a segment of the auditory nerve. The Cochlea is a spiral structure which has sensory receptors known ashair cells, that are responsible for detecting sound. Factors that contribute to hearing loss include genetics and environmental factors, such as exposure to loud noise and ototoxic medications. These factors can lead to atrophy of stria vascularis and loss of hair cells. 

Loss of hair cells

As mentioned earlier, hair cells are responsible for sound detection. They work by converting sound waves into electrical signals that the brain can interpret. Loss of hair cells leads to a reduction in the ability to hear and understand speech,  significantly impacting an individual's quality of life. When these hair cells are damaged or destroyed, they cannot be regenerated resulting in sensorineural hearing loss. 

Hair cell loss commonly occurs as a result of exposure to loud noise and ototoxic medications, as well as ageing. As we age, some hair cells naturally deteriorate and die, causing decline of our ability to detect high-frequency sounds, but it does not significantly affect our ability to hear. However, the most common and the most damaging cause of hair cell damage is exposure to loud sounds. When we are exposed to loud noise for an extended period of time or repeatedly, it can damage our hair cells, leading to permanent hearing damage. Also, short-term exposure to intense noise levels can cause temporary or permanent hearing loss. This type of hearing loss is known as noise-induced hearing loss and is prevalent among individuals who work in noisy environments, such as construction workers or musicians. 

Atrophy of the stria vascularis

The stria vascularis is a highly vascularised structure in the cochlea, which is responsible for regulating the right fluidncomposition for proper functioning of hair cells. Research shows that stria vascularis can independently degenerate with age. This event is known as atrophy of the stria vascularis and is the main cause of ageing deafness associated with genetics.  

Genetic factors

Environmental factors

Noise exposure

Exposure to loud noise can cause significant damage to the auditory system, resulting in hearing loss. The delicate hair cells in the inner ear are particularly vulnerable to damage from exposure to loud noise. Noise-induced hearing loss is a common occupational and recreational hazard that affects millions of people worldwide. Hair cells have tiny hair-like projections called stereocilia that bend and move in response to sound waves. When exposed to loud noise, these hair cells become damaged, leading to irreversible hair cell loss. 

Ototoxic medications

Ototoxic medications are drugs that can cause hearing loss by damaging the sensory hair cells in the inner ear. These medications can be classified into two categories: aminoglycosides and platinum-based chemotherapy drugs. Aminoglycosides are commonly used for treating bacterial infections, while platinum-based chemotherapy drugs are used to treat cancerous tumours. The mechanism of ototoxicity involves the inhibition of protein synthesis in the hair cells of the cochlea, leading to cell death.

Hearing loss caused by ototoxic medications can occur in two forms: temporary or permanent. Temporary hearing loss occurs when the drug is discontinued, and the hair cells recover. However, if exposure to the medication is prolonged or repeated, permanent hearing loss can result.

Symptoms of sensorineural hearing loss and aging

Sensorineural hearing loss can be classified into three categories based on  the range of hearing loss :

• Mild hearing loss - 26 to 40
• Moderate hearing loss - 41 to 55
• Severe hearing loss - 71 to 90

The condition usually affects both ears and appears gradually as an individual ages. The person might not notice the onset of hearing loss and might have to take necessary medical tests for a diagnosis.

Difficulty hearing high pitched sounds

An individual who struggles to hear high-pitched sounds will show the following symptoms:

• Difficulty to understand female and children’s sounds
• Not hearing birds’ chirping anymore 
• Struggling to hear device beeping
• Words with S, H, F and TH are harder to understand
• A sense of hearing people but not understanding them

The cause of not being able to hear high-pitched sounds with age is due to hair cells loss within the cochlea. 

Difficulty hearing conversations in noisy environments

Age-related hearing loss can also lead to difficulties hearing sounds in noisy places. For example, an individual struggles to follow a conversation in an environment with a background noise. This occurs because the ears of the affected person cannot filter the sounds. 

Tinnitus

Tinnitus is when you can hear the sounds which don't come from an external source, meaning that only the affected person can hear the sounds while others cannot. It is usually described as hearing buzzing, roaring, hissing, ringing and can vary in intensity and frequency. Tinnitus is associated with damage to the inner ear due to exposure to loud noise and age-related hearing loss. Damaged or stressed hair cells transmit altered signals to the brain causing noise heard only by the patient.

Difficulty hearing on the telephone

Phone calls are limited to a specific frequency range of 300-3400 Hz, which is insufficient for the broader frequency range of natural speech that spans from 250 to 8000 Hz. As a result, some parts of speech are compressed or omitted during transmission due to this frequency limitation. High-frequency sounds are crucial for clear speech and help distinguish similar-sounding words by resonating with important consonants. People with age-related hearing loss may find it challenging to follow phone conversations due to the combination of poor sound quality and hearing loss, leading them to perceive the speaker as mumbling.

Diagnosis of sensorineural hearing loss and aging

Hearing tests

There are a variety of tests that are done to support diagnosis of sensorineural hearing loss. 

Pure tone audiometry

The primary hearing assessment used to ascertain an individual's hearing threshold levels is pure-tone audiometry. This test helps in determining the degree, type, and configuration of a person's hearing loss, which forms the basis for diagnosis and management. Pure-tone audiometry relies on patient responses to pure tone stimuli and is considered a subjective behavioural measurement of hearing thresholds.

Speech audiometry

Speed audiometry test is used for assessment of how well an individual can recognise certain words in a noisy environment. It can check for the ability to understand speech. You will listen to a recording using headphones and be asked to repeat words you hear. It is a quick test that takes under an hour.

Tympanometry

Tympanometry is a test that examines the health of your middle ear by monitoring the movements of your eardrum. It is usually used to distinguish between two types of hearing loss: sensorineural and conductive. Tympanometry is performed by using a small device that is placed in the ear canal. The test takes only around two minutes for both ears.

Medical history and physical examination

When diagnosing an individual with any type of hearing loss it is important to do a physical exam and go through medical history. A doctor conducts a full head and neck examination, followed by an otological exam. Medical history will also help to determine what could potentially cause onset of hearing loss. It can include ear infections, surgeries, head traumas and exposure to loud noises, such as working in a loud environment.

Treatment of sensorineural hearing loss and aging

Treatment of sensorineural hearing loss includes usage of conventional hearing aids, cochlear implants or other assistive listening devices. Your doctor will help you to choose the right device depending on your test outcome and your lifestyle. 

Hearing aids

Hearing aids are small electronic devices that can help you to hear better through amplifying the sound. Hearing aids are worn either in or behind the ear depending on the type of device. They are common and easy to wear, however will require some time to get used to. 

Cochlear implants

Sometimes wearing hearing aids might not be enough to manage severe sensorineural hearing loss. In this case, hearing loss can be treated by cochlear implantation. Cochlear implant is an electronic device which is surgically inserted inside the inner ear and replaces the function of hair cells. It receives the sounds from outside and transforms them into signals which are sent to the brain via stimulation of the auditory nerve. 

Assistive listening devices

Assistive listening devices are those which support daily life by augmenting the sound and allowing you to hear better or those which use alternative ways of transmitting information. Examples of such devices include amplified telephones, TVs, vibrating alarms, doorbell alerts with flash, etc. 

Communication strategies

Implementing different communication strategies can help a person with hearing loss to communicate better and improve their ability to understand people. Here are some strategies that might be useful:

• Let other people know about your hearing loss and ask them to speak louder and more clearly
• Make sure that a person you are listening to is standing in front of the light and far from loud background noise. This strategy will allow you to see the speaker’s facial expressions and lips movements helping you understand them better
• Ask a speaker to repeat the sentence if you did not understand what was said

It is very important to be patient with a person who is affected by hearing loss, as it takes them a bit more time to process the information. Communication strategies are most effective if implemented by both a speaker and a listener with hearing loss.

Prevention of sensorineural hearing loss and aging

Unfortunately any type of sensorineural hearing loss is irreversible, hence it is extremely important to protect your ears throughout your life in order to prevent age-related hearing loss. Prevention techniques include avoiding loud sounds, wearing hearing protection, monitoring medication use and regular ear examinations. 

Summary

In the event that you experience indications of hearing loss due to ageing, it is recommended that you promptly consult with your GP. If left untreated, the likelihood of losing your ability to comprehend speech increases as your hearing loss progresses. Seeking early intervention can help preserve your hearing ability.