What is otosclerosis?
Otosclerosis can cause severe hearing loss and even complete deafness. How does this middle ear disease develop, what constitutes it, and how ENT doctors recognize and treat the disease? This article clarifies.
Otosclerosis is a middle ear disease. In advanced stages, the disease can also spread to the inner ear.
The prefix oto- comes from the Greek oũs (ous) meaning ear. Sclerosis is a thickening or hardening of organs and tissues.
In otosclerosis, an otherwise mobile bone that transmits sound to the inner ear hardens. The consequences range from hearing loss to deafness. In most cases, this is accompanied by low-pitched tinnitus.
To understand why ossification in the middle ear can have such serious consequences for our hearing, one must first understand how our ear works.
Sound travels to our ear through the air. The pinna conducts the sound through the ear canal to our eardrum. The sound causes the eardrum to vibrate. On the other side of the eardrum is a chain of small bones. The hammer, anvil and stirrup. These transmit the motion to a small membrane called the oval window. Behind the oval window is our inner ear. A bony cochlea filled with fluid. This is where our sensory hairs sit, which transmit a stimulus to the brain when the fluid moves, causing us to perceive a sound.
marked in blue: auditory canal; green: ossicular chain; orange: cochlea and organ of balance
In healthy ears, our ossicles can vibrate freely because they are connected at both ends with flexible membranes. In otosclerosis, the metabolism of the bone tissue at the oval window is disturbed. Growths occur that restrict the ability to move. As a result, not every movement of the eardrum reaches our inner ear. This is how conductive hearing loss develops.
Progression of the disease causes the ossicular chain to stiffen completely, which can then even lead to deafness.
"An enlargement of the previous illustration. Outlined in orange: The site of bone tissue proliferation."
Otosclerosis is noticeable by a gradual loss of high-frequency hearing, usually beginning in one ear. The patient does not feel pain, but over time the hearing loss increases and the other ear is affected. When the disease spreads to the inner ear, tinnitus and balance disorders may also be present. In this case, tinnitus is far more common than the rarely occurring balance disorders.
In a preliminary interview, the medical history, the patient is asked about previous diseases and cases in the family environment. If there are multiple cases of otosclerosis in your family tree, the risk that you will also develop the disease increases.
In otoscopy, the medical examination of the ear canals and eardrum, nothing can be detected in otosclerosis. Only when the disease is very advanced, a red spot on the eardrum can be observed. Usually, otoscopy serves to rule out other diseases, such as exostoses or otitis media.
An important part of the diagnosis is tonal audiometry - the hearing test. First, the patient is presented with soft sounds at different frequencies that get steadily louder. The client gives a sign as soon as the sound becomes quietly perceptible to him. The result of the test is the client's hearing threshold, i.e., the range above which the client perceives sounds is determined.
This test is supplemented by a second one. A so-called bone-conduction earpiece is placed on the patient's skull bone behind the ear. The vibrations from the earpiece travel through the skull bone directly into the inner ear, and the client perceives the sound. Again, as in the first test, the client gives a signal as soon as he perceives the sound. The result of the measurement is the hearing performance of the inner ear.
Typically in otosclerosis, there is a difference between these two hearing thresholds. The bone conduction threshold is at lower levels than the air conduction threshold. This is referred to as conductive hearing loss.
In addition, the ENT physician can examine the vibration ability of the eardrum in a tympanogram. Here, a probe is placed in the auditory canal, which on the one hand builds up pressure in the auditory canal and on the other hand emits a measuring tone. Otosclerosis reduces the eardrum's ability to vibrate.
If there is conductive damage, a low-pitched ringing in the ears is heard, and physical examination rules out otitis media, the diagnosis is considered confirmed.
"In red, we see the path that sound takes when it is transmitted via air conduction. In blue, on the other hand, the transmission via bone conduction."
The success of treatment depends on the progress of the disease at diagnosis. No cure is possible with medication.
Minimally invasive surgery is usually performed to remove the bone growth and insert a new stapes. 9 out of 10 patients report improvement or elimination of hearing loss after surgery. A common side effect is a feeling of dizziness, which subsides a few days after surgery.
At the first signs, the rule is: go to your trusted ENT practice as soon as possible and, if necessary, start treatment quickly.