What are the types of hearing loss?
There are three traditionally recognised types of hearing loss, however, in the recent past, one more overall type has vied for recognition. In the last few years a type of hearing loss called auditory processing disorder has become recognised. We will discuss it here, but first, let’s take a look at the three main types of hearing loss are:
- Sensorineural hearing loss
- Conductive hearing loss
- Mixed hearing loss
Sensorineural Hearing Loss
Sensorineural Hearing Loss is a problem of the inner ear or the nerve of hearing. It occurs when the cochlea, or the auditory nerve is damaged. Most sensorineural hearing loss is caused by damage to tiny hair cells in the cochlea. These hair cells are the nerves that send the electrical signals to the brain that the auditory cortex recognises as sound. When they are damaged, the information does not make it to the brain. Most types of sensorineural hearing loss are permanent.
Sensorineural hearing loss can have many causes, it can be genetic, caused by the aging process, diseases, exposure to loud noises, certain kinds of chemicals and medications and finally head injury.
Diagnosis of sensorineural hearing loss
A sensory hearing loss can be diagnosed with an audiometer and otoacoustic emission testing. A healthy cochlea emits measurable sounds when stimulated. If the sounds are absent or reduced, it suggests damage to the outer hair cells.
Treatment of sensorineural hearing loss
Damage to the hair cells of the cochlea cannot usually be treated with medication or surgery. There are no medical treatments for typical sensorineural hearing loss. At present, once the damage is done, it can’t be repaired. The only treatment available is using hearing Aids or cochlear implants. Hearing aids will help to reduce the impact of the hearing loss on your life. In some sudden-onset cases, steroids may be used to revive the cells. Typically, however, the treatment is hearing aids.
Auditory Processing Disorder
Without the brain, it is impossible to hear. The signal from the ears must be interpreted by the brain in order to be comprehended. In some cases, more often in smaller children, the auditory portion of the brain does not properly utilize the signals delivered by the ear. This is known as an auditory processing disorder. As we said, our awarenes of Auditory Processing Disorder (APD) has increased over the last few years. APD occurs when there is little or no hearing problems but the brain has problems processing the information contained in sound, such as understanding speech and working out where sounds are coming from. Many people who have APD have little or no hearing loss. At this stage, APD is little understood and there are no definitive treatment options. There are sound training options that seems to help train the brain to better process sound. Hearing aids are not an ideal solution in cases of APD, however, some people have reported improvements.
Diagnosis: Auditory processing disorders are typically diagnosed through a serious of audio test which evaluate the ability to understand in difficult situations, such as in the presence of competing sounds. Testing is time-intensive and may be accompanied by electrophysiological tests such as the ABR.
Treatment: Auditory processing disorders are most often treated by utilizing effective communication strategies. In the case of children, preferential seating and other accommodations at school may be warranted. In some listening situations, listening devices may be helpful.
VIIIth Nerve Tumor
Eustachian Tube Dysfunction
Once the auditory stimulus makes its way through the ear, it travels along the VIIIth cranial nerve to the brainstem and then up to the brain for processing. Sometimes, the ear may be healthy, but a significant hearing loss is caused by damage to the nerve itself. The most common type of neural hearing disorder is caused by a tumor on the VIIIth cranial nerve.
Diagnosis: Auditory brainstem response testing (ABR) is frequently used to rule out the presence of an VIIIth nerve tumor. However, an MRI is the gold standard. Suspicion of an acoustic tumor occurs when it manifests itself as a unilateral hearing loss, often accompanied by tinnitus and dizziness
Treatment: VIIIth nerve tumors are slow-growing and benign. Depending on the size, a physician may choose to simply monitor its growth. Tumors can also be removed surgically, but with significant risk to the auditory nerve. Hearing aids may also be helpful.
Conductive Hearing Loss
Conductive Hearing Loss is a problem of the middle or outer ear. More often than not, it occurs when there is a problem in the middle ear which interferes with the passing sound to the cochlea (inner ear). Conductive hearing loss can be caused by something as simple as too much ear wax. However, mostly the problem is caused by ear infections, punctured eardrums, abnormal bone growth in the Middle ear (otosclerosis). It is most common in children and because of problems in delivery of healthcare in indigenous populations.
More often than not, a conductive hearing loss can be medically treated. That treatment can vary from simple antibiotics to different surgeries. If a person does not want to undergo surgery, there are several types of hearing technology that can be used to treat the problem. Depending on the state of the outer ear, traditional hearing aids can help. If the state of the outer ear is such that traditional hearing aids are not the best option, well then bone conduction hearing aids and bone anchored hearing aids (BAHA) are the best options.
Eustachian Tube Dysfunction
Tympanic Membrane Perforation
The eustachian tube connects the space behind the eardrum to back of the throat. It’s purpose is to prevent the build up of air pressure behind the ear. The tube is typically close, but is designed to open with yawning and swallowing. Eustachian tube dysfunction is a condition where that tube either doesn’t open properly or doesn’t close properly. It can be caused by a muscle problem or excessive mucous.
Diagnosis: Dysfunction of the eustachian tube is usually symptomatically diagnosed by a physician and can be confirmed by an audiologist using an immittance bridge.
Treatment: Eustachian tube dysfunction is usually treated by medication designed to decreased the amount of mucous in the tube. Severe cases can also be treated with pressure-equalizing tubes or severing the muscle keeping the eustachian tube open.
Otitis media is an infection of fluid in the middle ear space. If the eustachian tube remains closed (see Eustachian Tube Dysfunction), significant negative pressure can build up behind the eardrum. That pressure can cause seepage from the surround tissue that may eventually fill the space behind the eardrum. The fluid prevents proper transmission of sound and can become infected if not drained.
Diagnosis: Otoscopy and tympanometry can be used to diagnose otitis media. A tympanogram tests the eardrums flexibility. If fluid is behind the eardrum, flexibility is significantly decreased.
Treatment: Otits media is often treated with antibiotics, which will treat the infection and alleviate the pain. However, antibiotics do not always permit proper drainage of the trapped fluid. In severe cases, an ENT surgeon will drain the fluid by placing a small incision in the eardrum.
Otosclerosis is a condition in which the movement of the middle ear bones is impeded. The footplate of the stapes (or stirrup) can become fixated, which prevents the proper transmission of sound. Otosclerosis often occurs gradually and is linked to family history.
Diagnosis: Otosclerosis can be diagnosed using tympanometry and the audiogram. Due to the fixation of the stapes, it affects air and bone conduction thresholds differently, which is manifested by a particular shape on the audiogram.
Treatment: Otosclerosis often warrants replacement of the stapes through surgery. In some cases surgery may be contraindicated, in which case, hearing aids can be very affective.
Tympanic Membrane Perforation
The tympanic membrane, also known as the eardrum, vibrates when sound hits it. It is comprised of three layers of skin and is water-tight. As one would expect, a hole in the eardrum sometimes prevents proper vibration and is usually perceived as a mild hearing loss.
Diagnosis: A tympanic perforation can often be seen by an otoscopic examination. It is confirmed using a tympanometer.
Treatment: Perforations often heal on their own, but not always. A tympanoplasty, or patching of the perforation, may be performed by an ENT surgeon.
Cerumen (Ear Wax) Impaction
Cerumen, or ear wax, is typically found in the outer third of the ear canal. It moisturizes the ear, repels insects, and traps dust. The hair of the ear canal naturally pushes the wax outward, where it can be easily wiped clean. Excessive hair, a small ear canal, or the use of Q-tips can disrupt this natural cleaning process and the wax can build up. If it completely blocks the ear canal, sound will not be able to get to the eardrum. Hearing loss caused by cerumen often occurs suddenly and is easily treated.
Diagnosis: An examination with an otoscope will reveal cerumen (instead of an eardrum). Tympanometry may be used to confirm that the wax is impacted.
Treatment: Use of a softening agent, such as Waxsol, may be required prior to removal. Cerumen can be removed by a curette (small spoon), suction system, or flushing with water.
Mixed Hearing Loss
A Mixed Hearing Loss occurs when both conductive hearing Loss and sensorineural hearing loss are present. Mixed hearing loss is relatively rare in the general population. The sensorineural part of the hearing loss is permanent, however, the conductive part can be permanent or temporary. In general, the treatment for this type of hearing loss is hearing aids. If there is a good possibility for treatment of the conductive element to be successful, well then it is worthwhile to consider treatment. However, even if the treatment is effective, the sensorineural part of the hearing loss will remain unchanged.