The auditory pathway is a complex network of structures that lead from the outer ear canal to the auditory cortex in the brain. An injury or pathology occurring anywhere along the auditory pathway could lead to hearing loss. The auditory pathway has four primary components: the outer ear, the middle ear, the inner ear, and the brain.
The outer ear includes the pinna, a cartilaginous structure on the side of the head, and the outer ear canal. The middle ear is composed of the tympanic membrane, also known as the eardrum, and the ossicular chain, or the three bones behind the tympanic membrane. The cochlea, or our organ of hearing, makes up the inner ear. The cochlea is a small snail shell-shaped structure that includes hundreds of thousands of “hair cells.” Finally, the inner ear is attached to the brain by the auditory nerve.
The pinna funnels sound waves into the ear canal. Those sound waves travel down to the eardrum, which causes it to vibrate. The fluid in the inner ear moves with the vibrations from the ossicular chain, stimulating the hair cells, which then send the signals to the brain through the auditory nerve.
Hearing loss can occur anywhere in the auditory pathway. If the cause of the hearing loss is the outer and/or middle ear, it is called conductive hearing loss. If the cause is within the inner ear, it is called sensorineural hearing loss. A combination of the two is called mixed hearing loss. Many diseases and disorders can cause hearing loss.
Diabetes and Hearing Loss
According to the American Diabetes Association, hearing loss is twice as common in individuals with diabetes when compared to those without diabetes.1 There are several correlations between diabetes and hearing loss. For example, chronic hyperglycemia, or an abnormally high level of sugar in the bloodstream, can lead to nerve damage throughout a person’s body and can cause damage to organs in the body. When the inner ear is impacted by hyperglycemia, signals are unable to be sent throughout the remainder of the auditory system.
Many patients with a history of Type 2 diabetes have secondary cardiovascular disease. Oxygenated blood is essential to the auditory system, particularly within the inner ear. If blood is unable to properly circulate through the inner ear, it may result in “anoxia,” or a lack of oxygen, to the structures. When anoxia occurs in the inner ear, postmortem histologic studies indicate significant damage to the hair cells.
In addition to cardiovascular disease, patients with Type 2 diabetes are at a higher risk for developing cancer and infections. The medications used to treat those diseases can be ototoxic (toxic to the ears). For example, many types of chemotherapies used to treat cancer, such as cisplatin, are known to be ototoxic. Many aminoglycoside antibiotics used to treat infections are ototoxic. Similar to ototoxic chemotherapies, aminoglycoside antibiotics cause damage to the inner ear, leading to hair cell death.
Childhood Infections and Hearing Loss
Viral infections that more commonly impact children can lead to sudden sensorineural hearing loss. These infections include but are not limited to, mumps, rubella, and herpes.4 If the infection results in hearing loss, it is typically unilateral, but it is not uncommon for a patient to develop bilateral sensorineural hearing loss. When a person is exposed to viral infections, the disease can travel through the blood supply to the inner ear, causing damage to the cochlear hair cells.
Osteoporosis and Hearing Loss
As a person ages, the skeletal bones are constantly breaking down and renewing. Individuals typically meet their peak bone density when they are in their 30s. After this, skeletal bones break down faster than they rebuild. Osteoporosis is a decrease in bone density, causing them to become weak and brittle. It is thought that hearing loss is associated with osteoporosis due to a breakdown in the temporal bone in the skull, or in the ossicular chain in the middle ear space.7 However, several other studies have found inconsistent results.
One meta-analysis used data from 52,828 participants to explore this possible correlation. The authors concluded that a decrease in bone density and formation of the temporal bone can cause physical changes to the inner ear. These changes can impact the ability of fluid to move through the cochlea, which may lead to sensorineural hearing loss.7
Multiple Sclerosis and Hearing Loss
A large portion of nerves in the central nervous system are coated in myelin. Multiple Sclerosis (MS) is a neurodegenerative disease that leads to a breakdown in the myelin sheaths, in addition to the nerve fibers themselves. When the myelin or nerves become damaged, signals are impaired from transmitting both to and from the brain. While hearing loss caused by MS is rare, the disease may damage the hair cells within the inner ear, or other structures in the auditory pathway such as the cochlear nerve and the auditory cortex within the brain.2
Meningitis and Hearing Loss
Surrounding the brain and spinal cord are three membranous layers called the meninges. Meningitis is an inflammation of the meninges caused by an infection. The majority of cases of meningitis are viral or bacterial in nature, but it can also be caused by parasites.
Meningitis may first present with flu-like symptoms, such as fever, nausea/vomiting, and fatigue. However, several other severe symptoms can appear. This includes, but is not limited to, a stiff neck, severe headaches, seizures, and confusion.3 Bacterial meningitis is deadly; without prompt antibiotic treatments, death can occur within days of symptom onset. Meningitis can affect those of all ages, but children under the age of 5 are the most vulnerable.5
The most common complication that occurs with meningitis is hearing loss. Approximately 10% of those who survive meningitis are left with permanent hearing loss.6 The hearing loss caused by meningitis is sensorineural in nature by damage to the hair cells within the inner ear or damage caused by inflammation of the auditory nerve.5
Acoustic Neuroma and Hearing Loss
Very rarely, slow-growing benign tumors can appear on the eighth cranial nerve (the auditory nerve). These are often called “acoustic neuromas.” While the tumors that grow on the vestibular (balance) portion of the auditory nerve are called “vestibular schwannomas,” they are often referred to by the collective term “acoustic neuroma.”
As previously mentioned, acoustic neuromas are benign tumors. One of the first symptoms of an acoustic neuroma is tinnitus – ringing in the ear. Due to the fact that acoustic neuromas almost always appear on only one side (unilateral), tinnitus is also unilateral. The other most common symptom of an acoustic neuroma is unilateral hearing loss. One study suggests that 85%-95% of patients with an acoustic neuroma have a diagnosable sensorineural hearing loss.4 Another common report of those with acoustic neuromas is balance dysfunction and/or vertigo.
Acoustic neuromas are rare – the incidence is approximately 1-2 in every 100,000 individuals in the United States.4 In order to determine if a patient has an acoustic neuroma, they must undergo a comprehensive audiometric evaluation, in addition to radiologic observations such as an MRI. There are three common treatment methods: surgical removal, radiation therapy, or observation. An ear nose and throat (ENT) physician working on a multidisciplinary team will determine the course of treatment.
Cholesteatoma and Hearing Loss
A cholesteatoma is a buildup of keratin-producing squamous epithelial cells behind the eardrum in the middle ear space.4 There are often very few symptoms that occur with a cholesteatoma until it is large enough to impinge on the ossicular chain. This causes conductive hearing loss. Bacteria can build up within the cholesteatoma, which can result in ear drainage, pain, and even erosion of the ossicular chain or mastoid portion of the temporal bone. Medical management for cholesteatoma may include observation, prescription antibiotics, and surgical removal.4
Ménière’s Disease and Hearing Loss
Ménière’s disease causes an increase in the production of fluid within the inner ear (endolymph). Ménière’s disease is a term for a collection of symptoms that occur as a result of increased endolymph: episodes of vertigo, fluctuating unilateral sensorineural hearing loss, unilateral tinnitus, and unilateral feelings of pressure or fullness.4
Ménière’s disease typically occurs unilaterally, but as time progresses, 17%-50% of patients will also develop Ménière’s disease of the opposite ear.4 There are various treatment methods used for patients with Ménière’s disease, and the treatment route is determined by the severity of the disease. A physician may prescribe vestibular suppressants and antiemetics for the episodes of vertigo, and an audiologist may recommend hearing aids to treat the hearing loss. One common conservative treatment method for Ménière’s disease is a low-salt diet and diuretics to decrease the endolymphatic fluid pressure. A person with Ménière’s disease may be a candidate for surgery. The surgery can include the placement of a shunt in the inner ear to drain the endolymph, or something more severe such as the destruction of the vestibular portion of the impacted ear.4
Otosclerosis and Hearing Loss
The most common cause of adult conductive hearing loss is otosclerosis. In the middle ear space are three bones called the ossicular chain that connects the eardrum to the inner ear. When the smallest of the ossicles (the stapes) becomes fixed to the inner ear, this results in otosclerosis. Severe and progressive otosclerosis can result in damage to the inner ear. There is typically a genetic component to otosclerosis; meaning that if a patient has a family history of otosclerosis, they are at a higher risk than patients who do not have a family history.4 Otosclerosis is often treated with hearing aids to overcome conductive hearing loss. Surgery may also be recommended, in which the stapes are altered or replaced to reduce hearing loss.4
Can ear wax buildup lead to hearing loss?
Yes, ear wax build up can potentially cause hearing loss. When ear wax accumulates and becomes impacted in the ear canal, it can block sound waves from reaching the eardrum, resulting in reduced hearing ability. It’s important to address excessive ear wax promptly.
However, other factors like infections, certain medical conditions, and exposure to loud noises can also contribute to hearing loss. If you’re experiencing changes in your hearing, it’s advisable to consult with an audiologist for a proper evaluation and personalized recommendations to address the underlying issue.
What is the treatment for hearing loss caused by diseases?
The type of disease and following auditory injury and pathology determines the course of treatment. For example, those who experience sudden sensorineural hearing loss due to the disease may require antibiotics and steroids. Patients that develop conductive hearing loss, such as from otosclerosis, may benefit from surgical procedures to repair the ossicular chain.
How does age affect your risk of developing hearing loss from a disease?
The diseases discussed in this article have the ability to impact those of all ages, but some age groups may be at a higher risk than others. As previously stated, children under the age of 5 are the most vulnerable to developing meningitis. However, osteoporosis and otosclerosis are more common in adults over the age of 30.4
How can you protect your hearing from disease-related damage in the future?
Regular visits with a primary care provider and an audiologist is essential. If a person is more genetically or environmentally at risk for developing a hearing loss, their hearing status should be checked consistently for any changes that may occur.
References
1American Diabetes Association. (2022). Diabetes complications: Diabetes and hearing loss. American Diabetes Association. https://diabetes.org/diabetes/diabetes-and-hearing-loss
2Di Stadio, A., Dipietro, L., Ralli, M., Meneghello, F., Minni, A., Greco, A., Stabile, M. R., & Bernitsas, E. (2018). Sudden hearing loss as an earlier detector of multiple sclerosis: A systematic review. European Review for Medical and Pharmacological Sciences, 22.
3Mayo Clinic. (2022). Diseases and conditions: Meningitis. The Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/meningitis/symptoms-causes/syc-20350508
4Musiek, F. E., Baran, J. A., Shinn, J. B., & Jones, R. O. (2012). Disorders of the auditory system. Plural Publishing, Inc.
5National Deaf Children’s Society. (2022) Causes of deafness: Meningitis. National Deaf Children’s Society. https://www.ndcs.org.uk/information-and-support/childhood-deafness/causes-of-deafness/meningitis/
6Richardson, M. P., Reid, A., Tarlow, M. J., & Rudd, P. T. (1997) Hearing loss during bacterial meningitis. Archives of Disease in Childhood, 76.
7Upala, S., Rattanawong, P., Vutthikraivit, W., & Sanguankeo, A. (2017). Significant association between osteoporosis and hearing loss: A systematic review and meta-analysis. Brazilian Journal of Otorhinolaryngology, 83.
