Hearing loss

Hearing loss

The global impact of hearing loss

The World Health Organization (WHO) estimates that around 5% or 430 million people worldwide have disabling hearing loss, with this number expected to nearly double by 2050 (1). In South Africa, 2,2% of urban school children needs follow-up treatment for hearing loss (2).

Hearing loss has significant social and economic impacts, as people with hearing loss face communication barriers, limited access to education and employment opportunities, and increased risk of isolation and mental health issues.

The sound conduction mechanism

Sound conduction through the ear and to the brain involves a complex process that includes the outer, middle, and inner ear and the brain.

The outer ear consists of the pinna, ear canal, and eardrum. Sound waves enter the outer ear through the pinna and travel down the ear canal. The sound waves then hit the eardrum, causing it to vibrate.

Left eardrum (tympanic membrane)
Left eardrum (tympanic membrane)

These vibrations are then transmitted to the middle ear.
In the middle ear, the vibrations from the eardrum are amplified by the three tiny bones called the ossicles – the malleus, incus, and stapes. These bones work together to amplify the vibrations and transmit them to the inner ear.

The three human ossicles namely the malleus (M), incus (I) and stapes(S).
The maleus (M), incus (I) and stapes (S)

The inner ear is made up of the cochlea, which is a spiral-shaped tube filled with fluid. When the amplified vibrations from the middle ear reach the cochlea, they cause the fluid in the cochlea to move. This movement stimulates tiny hair cells within the cochlea, which then convert the mechanical energy of the sound waves into electrical signals. These electrical signals are then sent to the brain through the auditory nerve.

The stapes, inner ear and nerve
The stapes, inner ear and nerve

The auditory nerve carries the electrical signals to the brainstem, where they are processed via the cochlear nucleus, superior olivary complex, lateral lemniscus and inferior colliculus and then sent to the auditory cortex in the brain. The auditory cortex interprets electrical signals as sound and gives meaning to the sound we hear.

Auditory brainstem pathways (source: Wikipedia)
Auditory brainstem pathways (source: Wikipedia)
The auditory cortex in the brain (source: Wikimedia Commons)
The auditory cortex in the brain (source: Wikimedia Commons)

Types of hearing loss

There are five types of hearing loss:
· Conductive hearing loss
· Sensorineural hearing loss
· Mixed hearing loss
· Central hearing loss
· Pseudo hearing loss

Conductive hearing loss

Conductive hearing loss is a type of hearing loss that occurs when sound waves are not able to reach the inner ear due to a blockage or obstruction in the outer or middle ear. This can result from various factors such as ear infections, earwax buildup, punctured eardrums, or structural abnormalities in the ear.

A few examples of conditions that can cause conductive hearing loss include otitis media (middle ear infection), otosclerosis (abnormal bone growth in the middle ear), cholesteatoma (abnormal skin growth in the middle ear), and a foreign object stuck in the ear canal. Individuals with conductive hearing loss may experience muffled or distorted sounds, difficulty hearing faint sounds, or feeling like their ear is blocked.

Treatment options for conductive hearing loss may include medication, surgery, or hearing aids, depending on the underlying cause.

Sensorineural hearing loss

Sensorineural hearing loss is when there is damage to the inner ear or nerves that are responsible for transmitting sound to the brain. This hearing loss can be caused by ageing, exposure to loud noises, certain medications, genetics, or diseases like Meniere’s disease or meningitis.

Examples of sensorineural hearing loss include presbycusis, which is age-related hearing loss that occurs as a result of the natural ageing process and noise-induced hearing loss, which is caused by exposure to loud noises over a prolonged period. Another example is ototoxicity, which is hearing loss due to the toxic effects of certain medications or chemicals on the inner ear. People with sensorineural hearing loss may experience difficulty hearing faint sounds, understanding speech in noisy environments, or hearing high-pitched sounds.

Treatment options for this hearing loss may include hearing aids, cochlear implants, or assistive listening devices.

Mixed hearing loss

Mixed hearing loss is a type of hearing impairment that occurs when an individual experiences sensorineural hearing loss (damage to the inner ear or auditory nerve) and conductive hearing loss (a problem with the outer or middle ear). This means that sound waves are not effectively transmitted to the inner ear and processed by the auditory nerve, resulting in difficulties with both loudness and sound clarity.

Some conditions that can lead to mixed hearing loss include age-related hearing loss, ear infections, trauma to the ear, genetic factors, and exposure to loud noise. Individuals with mixed hearing loss may have trouble understanding speech, hearing conversations in noisy environments, and detecting sounds at various frequencies.

Treatment options for mixed hearing loss may include hearing aids, cochlear implants, or medical interventions, depending on the specific underlying causes

Central hearing loss

Central hearing loss is a type of hearing loss resulting from damage or dysfunction to the central auditory nervous system, specifically the brainstem or auditory cortex. This type of hearing loss differs from the more common sensorineural or conductive hearing loss, which is caused by ear or auditory nerve issues.

Examples of central hearing loss can include auditory processing disorder, where the brain has difficulty processing and interpreting sounds correctly, leading to difficulties in speech understanding and communication. Another example is Wernicke’s aphasia, a language disorder that can be caused by damage to the brain’s left temporal lobe, leading to difficulties in understanding spoken and written language.

Central hearing loss can significantly impact an individual’s ability to communicate and interact with others and may require specialized treatment and therapy to manage effectively

Pseudo-hearing loss

Pseudo-hearing loss is a condition where an individual experiences symptoms of hearing loss without any actual impairment of the auditory system. This can be caused by psychological factors, such as stress, anxiety, or conversion disorder, rather than physical damage to the ears.

Some examples of pseudo-hearing loss include individuals who believe they cannot hear specific frequencies, even though their hearing tests indicate normal results. They may also complain of hearing loss in social or conversational settings but have no difficulty hearing in other environments. Additionally, those with pseudo-hearing loss may exhibit inconsistent responses during hearing tests, leading to confusion for the individual and healthcare providers.

Pseudo-hearing loss highlights the complex connection between the mind and the perception of sound and the importance of considering psychological factors in evaluating and treating hearing-related issues.

Surgical options to correct hearing loss

Surgical options to treat hearing loss encompass various approaches aimed at eradicating disease, reconstructing the natural hearing system, or providing alternative solutions to improve hearing function. Eradication of disease typically involves procedures such as tympanomastoid surgery to address underlying infections or tumours affecting the auditory system. This may include removal of diseased tissue or drainage of infected fluid to restore normal hearing function.

Reconstruction of the natural hearing system may involve a procedure like tympanoplasty. A tympanoplasty is the repair of a tympanic membrane perforation, a cause of conductive hearing loss. Reconstructions can effectively treat conductive hearing loss caused by abnormalities in the middle ear.

A tympanic membrane peforation
A tympanic membrane peforation

Passive middle ear implants are another option for those with conductive hearing loss, where a device is surgically implanted to bypass damaged or non-functioning components of the middle ear, allowing sound to be transmitted directly to the inner ear.

A total ossicular replacement prosthesis (TORP) made of titanium. Courtesy: Spiggle & Theis.
A total ossicular replacement prosthesis (TORP)

Implantable bone conduction hearing aids are another surgical option that bypasses the middle ear altogether by transmitting sound vibrations directly to the inner ear through bone conduction. This can be effective for individuals with conductive hearing loss or single sided deafness.

implantable hearing solutions - vibrant soundbridge
A bone conduction implant (courtesy : MEDEL)

Active middle ear implants involve surgically placing a device in the middle ear to enhance sound transmission to the inner ear. This can be useful for individuals with conductive, mixed or sensorineural hearing loss who have not benefited from traditional hearing aids.

implantable hearing solutions - bonebridge
An active middle ear implant (courtesy : MEDEL)

Cochlear implants are a surgical option for individuals with severe to profound sensorineural hearing loss, where an electronic device is implanted in the cochlea to bypass damaged hair cells and stimulate the auditory nerve directly.

implantable hearing solutions - cochlear implants
A cochlear implant system

Auditory brainstem implants (ABI’s) are used for individuals who are not candidates for cochlear implants due to cochlea or auditory nerve abnormalities. This involves placing an electrode on the brainstem to restore hearing function. In South Africa ABI’s are performed in only two centers, namely Johannesburg and Cape Town. Dr Hofmeyr does nor perform ABI surgery.

Overall, surgical options for treating hearing loss aim to restore or improve auditory function through a variety of approaches tailored to the individual’s specific needs and underlying causes of their hearing loss. Dr Hofmeyr can offer the majority of these options to his patients