Hearing Healthcare Education

Causes of Sensorineural Hearing Loss

Age-Related Hearing Loss (Presbycusis)

At some point, everyone who lives long enough will develop some age-related hearing loss. For some it happens sooner rather than later. Typically, men tend to develop hearing loss sooner, and it tends to be more severe than in women due to noise exposure and other environmental conditions. It is believed that being exposed to “normal, everyday noise levels” may accumulate over time and make our ears more vulnerable to aging. Other factors that may also contribute are smoking, poor diet, infections, high fevers, certain medications, and health conditions such as heart disease, diabetes, and high blood pressure.

Loud Noise Exposure

This is the second most common cause of hearing loss. It is a noisy world we live in. Over time, repeated exposure to noise wears out the hair cells within the cochlea. When enough of these hair cells are gone, we develop hearing loss.  This generally happens very gradually so the person is not aware until the damage has already been done. On the other hand, there is another type of noise exposure: acoustic trauma. This is when an extremely loud burst of sound happens, such as a gunshot or explosion. This can cause a rupture of the eardrum, fractures of the tiny bones in the ear, and/or partial or complete destruction of the hair cells within the cochlea.

Hereditary Hearing Loss

In this case, the degree by which noise, aging, toxins, and other factors affect each individual seems to be related to their genetic makeup. Two people could be subjected to the same noise level for instance, but one may not develop hearing loss because they are less susceptible. There is also dominantly inherited hearing loss. Usually a person with this type of hearing loss will have a parent with a similar loss.

Ototoxicity

This is hearing loss related to certain medications. Currently there are more than 200 potentially ototoxic medications on the market. Some are prescription only and some are over the counter, such as aspirin (salicylates), although the hearing loss from high doses of aspirin is usually temporary. Some antibiotics (aminoglycosides), quinine, anti-inflammatory drugs (ibuprofen, etc.) and loop diuretics can also cause temporary or permanent damage depending on the dosage and length of time taken.  Cisplatin, a chemotherapy drug, is the most ototoxic drug in clinical use that has the potential to cause hearing loss. It’s important to have your hearing checked prior to, during, and after treatment.  Early signs of ototoxicity can include onset of tinnitus, balance problems, beginning or worsening hearing loss, and more.

Other causes of sensorineural hearing loss include Ménière’s disease, labyrinthitis (inflammation of inner ear), auditory neuropathy, and acoustic tumors.

"How Do We hear?"

The answer is: with our brains. Yes, the ears are the avenue for sound, but it’s the brain that interprets and makes sense of the signal so that we know what we “hear.”

First, sound waves enter through the outer ear and travel through the ear canal to the middle ear where sound waves are amplified.

Ear Anatomy

The middle ear consists of the eardrum (tympanic membrane), three small bones known as the hammer (malleus), anvil (incus), and stirrup (stapes). When the sound waves hit the eardrum, it vibrates, causing the hammer to move, which then moves the anvil, which in turn moves the stirrup, causing vibrations in the inner ear. This is the mechanical part of our hearing. If there is a disruption in this process, there may be significant (conductive) hearing loss.

The inner ear consists of the cochlea and the hearing nerve.  Vibration of the stapes footplate against the membrane of the oval window creates waves in the perilymph (fluid) within the cochlea. This is the hydraulic part of the process. Within the cochlea, frequencies are sorted and analyzed by tiny hair cells (cilia). Then energy (power) of these sound vibrations are converted into neural (nerve) impulses that travel through the cochlear nerve to the brain, allowing us to hear.

If there is a disruption or degradation of the hair cells, then this process becomes distorted, resulting in hearing loss (sensorineural or nerve damage).

As you can see, this is a very complex and intriguing process. If you would like to know more about this and how hearing aids can help to regain sound and better understanding, we encourage you to visit us for a complimentary hearing screening.

"What can go wrong with my hearing?"

There are many different things that can cause hearing loss as well as different types and degrees of hearing loss. Below is a list of some of these different causes of hearing loss with explanations.

  • Cerumen - ear wax blocking the ear canal.
  • Perforated tympanic membrane – a hole in the eardrum.
  • Barotrauma – fluid collects in the middle ear when the Eustachian tube does not open properly, usually after flying or diving.
  • Otitis media – the presence of fluid in the middle ear.
  • Suppurative otitis media – an infection of the middle ear caused by bacteria from a cold or other respiratory infections. Germs enter the middle ear through the Eustachian tube, and the tube becomes blocked, trapping fluid in the middle ear. This can be acute or chronic.
  • Otosclerosis – spongy changes in the bony capsule around the inner ear that can harden and become sclerotic. The stapes can then lose its mobility, which can cause significant hearing loss because the mechanical transmission of sound waves is interrupted. This disease is inherited and occurs more often in women.
  • Cholesteatoma – a tumor occurring in the middle ear. As it grows, it causes serious infections and may destroy bone and other tissue. An odorous discharge is usually present as well a feeling of fullness, earache, and dizziness.
  • Ossicular discontinuity or fixation – the tiny bones (hammer, anvil, stirrup) no longer fit together properly or become “stuck” due to a head trauma, loud noise, or osteoarthritis.

"Why is it I hear things but cannot understand them?"

This relates to the basics of how we hear (see above). Within the cochlea, frequencies are sorted and analyzed by tiny hair cells and converted to neural (nerve) impulses. If there is a disruption or degradation, this process becomes distorted and results in hearing loss, especially in the high frequencies.

Specifically, hearing loss caused by the aging process is a gradual loss over a period of many years. Some of the hair cells have died or become damaged, and the brain is not receiving a good signal to work with. As a result, we just get parts of the words or conversations.

The brain can only interpret information it has previously received/learned, such as a sound or language. Considering this, no matter how good or precise your hearing is, you cannot understand a foreign language unless you have learned it.

If you have difficulty understanding speech, or it seems that people mumble, then you should have your hearing checked. If hearing loss is indicated, and you’re a candidate for hearing aids, then the hearing aids will amplify the frequencies necessary to give your auditory system as much information as possible to support better speech understanding. Without treatment, the condition will likely worsen. The longer your brain is deprived of the auditory stimulus, the more difficult it is to treat.

See us today for a free hearing consultation.

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