Otosclerosis affects the bones of the middle ear that conduct sound. Sometimes called otospongiosis, it’s one of the most common causes of progressive hearing loss in young adults. What triggers otosclerosis is still uncertain. This disease is thought to be passed down through families, as it is frequently seen in those affected. Even if a family history of otosclerosis is present, the risk of developing the disease isn’t always zero.
Some basic facts
Otosclerosis affects more Americans than the population of the entire state of Nevada. However, it appears that the prevalence is decreasing.
Otosclerosis is more common in white women and Caucasians of European descent, who are known to have a genetic component. In the United States, about one in 10 Caucasian adults develop otosclerosis, with the risk to white women twice as high.
Generally, if someone has a parent with otosclerosis, they have a 25 percent chance of developing it as well. The risk jumps to 50 percent if both parents have the disorder, experts approximate. Although otosclerosis is more common in people of African, Native American, and Asian descent, it is much less common in the general population of these groups of people.
Otosclerosis also tends to be a younger person’s disease. Symptoms typically crop up between the ages of 10 and 45 and most commonly during a person’s twenties. The disorder’s toll usually rises around the time of one’s mid-thirties, but this is not always the case. While otosclerosis can lead to severe hearing loss, it rarely results in total deafness.
People with otosclerosis often are unaware that they have the disorder until they experience hearing loss, which gradually worsens. Unlike noise-induced hearing loss—which first affects the ability to hear high-frequency sounds—otosclerosis more often causes difficulty with low-pitched, deeper sounds or whispering.
Otosclerosis patients may speak softly because they believe their own voices are too loud for them to hear. And many people with otosclerosis say it’s easier for them to follow conversations in noisy environments—perhaps because others are speaking more loudly and in higher-pitched voices. Although it usually begins in one ear, otosclerosis usually affects both of the ears.
Otosclerosis’ mechanism of action
Otosclerosis involves an abnormal overgrowth of bone that prevents one of the tiny bones in the middle ear from vibrating like it should. This reduces sound transmission to the inner ear, resulting in hearing loss due to conductive causes.
It’s the tiniest bones in your body: a chain of three auditory ossicles connect the middle and inner bones to the ear. They’re the malleus (hammer), incus (anvil), and stapes (stirrup), each bearing a Latin name that describes its shape.
As the smallest bone in the auditory ossicles, the stapes is also the most commonly affected by otosclerosis, measuring only 3 x 2.5 mm in diameter.
The auditory ossicles consist of three bones, each of which plays an important role in the process of hearing. For hearing to occur, sound waves must collect in the outer ear, pass through the ear canal, and cause the eardrum to vibrate. The inner ear receives these vibrations via the auditory ossicles and continues the hearing process there.
Right beside these tiny bones is the otic capsule, a rigid and extremely dense outer wall within the temporal bone that protects the inner ear. The otic capsule is the hardest bone in the human body.
Otosclerosis starts in this area when bone tissue of the otic capsule begins to grow abnormally. In the beginning, the growing bone is soft and malleable (otospongiosis). But with time, the soft areas scar and harden (otosclerosis) .
When abnormal bone tissue growth and scarring extends onto and around the stapes—or other small bones of the adjacent middle ear—it hinders their ability to vibrate and conduct sound, resulting in hearing loss and conductive hearing.
Much less frequently, the scarred bone tissue from otosclerosis affects the inner ear, impinging nerve function there and resulting in sensorineural hearing loss and sometimes balance issues. Otosclerosis can cause hearing loss in either the inner ear’s cochlea or auditory ossicles (conductive hearing loss) or both, causing a loss known as mixed hearing loss (sensorineural hearing loss).
Bone remodeling, a lifelong process that involves the body’s self-renewal of bone tissue, is true. But in otosclerosis, this bone remodeling goes awry. When it continues to progress, the result is hearing loss, which typically worsens over time.
Usually, people only realize they have otosclerosis after the abnormal bone growth has reached the stapes or the other auditory ossicles, causing hearing loss. Doctors refer to this as clinical otosclerosis, meaning the person shows symptoms of the disorder.
Patients with otosclerosis may be unaware they have it because the disease has not progressed far enough for symptoms to appear. Experts call this histological otosclerosis, and it occurs more frequently than clinical otosclerosis.
The story behind otosclerosis
While the medical and research communities understand what happens to the ear as a result of otosclerosis, what actually triggers the disorder remains uncertain. The current consensus is that multiple factors may be at play in the development of the disease, and that the genetic component alone may not be sufficient to set it in motion. Many experts believe that otosclerosis must be triggered by a combination of genetic, environmental, hormonal, and/or other factors.
Research suggests that otosclerosis may be linked in some way to the following:
- Genetics: Otosclerosis tends to run in families. Many (perhaps as many as 50%) of those who suffer from the disorder have a gene associated with it. Statistics also show that there’s a 25 percent chance of developing otosclerosis if one parent has it and twice that (50 percent ) if both parents have it. What remains to be answered is why otosclerosis isn’t passed down through generations in families where it has been present. And why do some people who have no known family history of the disorder end up developing it? The genes that cause otosclerosis are still being studied in an effort to better understand the disease.
- Pregnancy: There appears to be a pattern in which women first show signs of otosclerosis during or immediately after pregnancy. For these women, hearing loss seems to come on more rapidly. In fact, women with otosclerosis in both ears felt they experienced a 33 percent decline in their hearing after a single pregnancy, one study found. Study participants also noted greater decline with each subsequent pregnancy. Pregnancy-induced hormonal changes, say experts, could exacerbate otosclerosis.
- Mumps and other viral infections: Some experts believe that otosclerosis and the measles may have a viral connection. They suspect that the viral infection triggers the disorder. Research conducted on bone and tissue samples taken from the ears of people with otosclerosis has found evidence of the measles virus, although not in all samples. Additionally, studies show that measles vaccination reduces the risk of developing otosclerosis.
- Trauma and stress fractures: Experts have suggested that stress fractures to bones in the ear, and to the bony tissue surrounding the inner ear in particular, may put people at an increased risk of developing otosclerosis.
- Autoimmunity: Some researchers believe that otosclerosis may be linked to an autoimmune response by the body. This type of response generally happens when the person’s immune system becomes confused, acting against healthy body tissue as if it were a pathogen. The body’s autoimmune response is frequently triggered by a combination of environmental and genetic factors.
Otosclerosis is unquestionably a complicated condition. And both the intricacy and relative inaccessibility of the inner ear raise additional challenges in fully understanding it.
Living with otosclerosis
When a young person begins to notice they’re losing their hearing, it can be a very confusing and overwhelming time. It’s critical that they consult with qualified medical professionals in order to receive an accurate diagnosis.
Anyone who experiences hearing loss should see an otolaryngologist (an ear, nose, and throat doctor, or ENT), otologist, and/or audiologist.
If the person experiences low-pitched hearing loss, falls within the demographics of those at greater risk of otosclerosis, and/or is aware of hearing loss in any member of the extended family, they should ask the hearing health provider about otosclerosis specifically and about their experience in diagnosing it.
An otoscope, hearing tests, and a computerized tomography (CT) scan may all be used in the hearing of diagnosing ear, in addition to the patient’s medical history and the health history of their family. Ruling out other health issues that potentially could cause the same symptoms is an important part of the diagnostic process as well.
Proven Methods of Care
Treatment for otosclerosis depends on the person’s specific circumstances, the degree of the symptoms, and decisions made together by the doctor and individual.
Otosclerosis has been treated and/or managed in various ways, including the following:
Watch and wait: Otosclerosis will progress to different degrees and at different rates for different people. Not everyone with otosclerosis goes on to develop moderate to severe hearing loss. The disorder may progress more slowly for some people. Depending on the degree of hearing loss, the person’s health, and other individual factors, hearing care professionals may recommend a watch and wait approach. Regular hearing tests are usually part of this regimen.
Hearing aids: Many people with otosclerosis use hearing aids to help compensate for the hearing loss. Hearing aids boost sound volume and can be customized to meet the individual’s hearing needs. New models also provide many useful features. Licensed hearing care professionals can coordinate with the individual’s physician and advise the person with otosclerosis on hearing aid types and technologies that are most appropriate for their individual needs.
In addition to hearing aids, there may be supplemental assistive devices that can help people with otosclerosis hear better in their day-to-day lives. Qualified hearing healthcare professionals can guide individuals on the usefulness and appropriateness of such devices.
Sodium fluoride supplements: Some doctors prescribe these dietary supplements in certain doses and according to specific schedules in the hope of slowing the progression of the disease. Due to limitations in existing research, however, experts continue to debate the effectiveness and appropriateness of using these supplements.
When the otosclerosis has progressed to a certain point, the doctor may consider a specialized surgery known as a stapedectomy. The affected stapes is removed and replaced with a prosthesis—an artificial stapes—that is designed to perform the same function in the hearing process as the natural one. Specialists consider many individual factors before recommending this surgery.
Currently, there is no drug treatment for otosclerosis. The search for safe and effective pharmacological treatments for this disorder continues, however.
Managing otosclerosis in daily life
Having otosclerosis can be a frightening diagnosis for a young person who has no family history of the disease to prepare for. If you have otosclerosis, you should talk to your doctor about how you can get the help you need. Following a healthy lifestyle generally helps people better manage the stress associated with any hearing disorder.
Reducing tension, getting enough sleep, and avoiding nicotine and other harmful substances are all part of a healthy lifestyle, as is managing stress and engaging in regular physical activity, if medically feasible. Addressing a person’s hearing loss, no matter what the cause, is generally considered a positive life change.
The NIDCD funds a variety of otosclerosis-related studies.
The complicated architecture of the inner ear makes it difficult for scientists to study this part of the body. Because researchers can’t remove and analyze a sample of the inner ear from someone who has otosclerosis (or other hearing disorders), they must study ear bone samples from cadavers donated for research.
There is a scarcity of these so-called temporal bone samples. To encourage more research on otosclerosis, the NIDCD supports national temporal bone collections, such as the Otopathology Research Collaboration Network at the Massachusetts Eye and Ear Infirmary.
This effort coordinates the collection and sharing of temporal bone tissue among laboratories. It also encourages scientists to combine modern biology, imaging, and computer technologies with information from patient history and pathology reports to look for new clues and solutions to ear disorders caused by bone abnormalities.
Research on genetics and bone remodeling is also supported by the NIDCD, which aims to better understand the causes of otosclerosis and investigate new treatments. NIDCD-supported researchers are currently testing—in animals—the effectiveness of an implantable device that can deliver a bone-growth inhibiting drug directly into the inner ear to correct the bone abnormalities that cause otosclerosis. If the results are encouraging, further testing will be conducted on humans.
Is there a test for otosclerosis?
Otosclerosis is diagnosed by health care providers who specialize in hearing. These include an otolaryngologist (commonly called an ENT, because they are doctors who specialize in diseases of the ears, nose, throat, and neck), an otologist (a doctor who specializes in diseases of the ears), or an audiologist (a health care professional trained to identify, measure, and treat hearing disorders) (a health care professional trained to identify, measure, and treat hearing disorders).
The first step in a diagnosis is to rule out other diseases or health problems that can cause the same symptoms as otosclerosis. Hearing for hearing sensitivity and middle-ear sound conduction (audiograms) are the next steps (tympanogram). Otosclerosis can be diagnosed with imaging tests such as a CT scan.