Clinical picture, diagnosis & treatment
Otosclerosis is a medical condition that afflicts the bony labyrinth in the inner ear. This causes inflammatory bone remodeling processes (otospongiosis), followed by bone ‘hardening’ (sclerotization). This is frequently accompanied by ossicular chain hardening, which in turn leads to conductive hearing loss.
Surgical or medicinal treatment is performed in some cases. If this is impossible, hearing aids will be used to help alleviate the hearing impairment and give you back your quality of life.
The clinical picture
This illness occurs most frequently between the ages of 20 and 50. For better comprehension, take a look at the exact structure of the ear: Otosclerosis usually starts in the bony labyrinth, a bony cavity located in the inner ear. The inner ear consists of the cochlea and the vestibular system. The actual hearing process takes place in the cochlea. If otosclerosis has become so advanced that the cochlea is affected, it can lead to sensorineural hearing loss. As described above, numerous otosclerosis patients also suffer from a hardened ossicular chain.
The ossicular chain is located in the middle ear and consists of three separate little bones which are flexibly interconnected. These are known as the hammer (malleus), anvil (incus) and stapes (stirrups). The latter verges on the inner ear and is therefore most frequently affected by otosclerosis. The ossicular chain’s main function is to amplify the force of sound vibrations. If otosclerosis has caused the ossicular chain to stiffen, the sound from outside can no longer be adequately conducted to the inner ear, resulting in conductive hearing loss.
Symptoms may vary, depending on the location of otosclerosis in the ear. As briefly described above, the ossicles are usually affected, which most frequently results in slowly progressing conductive hearing loss. In approximately 30% of the cases, both ears may be affected. A second important symptom is buzzing in the ears (tinnitus), usually with a low noise pattern. In rare cases, otosclerosis affects the cochlea, resulting in hearing impairment of the inner ear, which if severe, can lead to complete deafness.
Causes of otosclerosis
The causes of otosclerosis are still unknown. However, genetics is believed to be a factor, as afflicted persons frequently have a family history of otosclerosis. Hormonal levels can also play a role in causing otosclerosis. Women are far more frequently affected than men, and the illness usually appears during pregnancy and childbirth.
The diagnosis can usually be confirmed with two to three different examination procedures:
- Gellé test
In this test, the examiner strikes a tuning fork and places it on the crown of the patient’s head, similar to the Weber test. The examiner then creates overpressure in the external ear canal which artificially hardens the ossicular chain. Following the artificial hardening of the ossicular chain, a patient with normal hearing will hear the sound of the tuning fork as softer than before. In contrast, an otosclerosis patient will not perceive any difference in sound volume, as his ossicular chain is already hardened due to the illness.
- CT examination (computerized tomography)
The CT examination confirms the diagnosis of a rare cochlear form of otosclerosis. Computed tomography can make the bone remodeling processes visible.
- Pure-tone audiometry
During this hearing test, patients are subjected to high and low tones, each at different volumes. The patient will signal as to when he is barely able to hear the tone. This creates an auditory threshold curve (for air conduction). In bone conduction, the sound vibrations are transferred to the inner ear via the cranial bones, bypassing the middle ear. Bone conduction is therefore used to assess the efficiency of the inner ear separately from the external ear canal and the middle ear. If pure-tone audiometry is now conducted on an otosclerosis patient, the auditory threshold curve for air conduction reduces with every tone frequency. This is due to the hardened ossicles and associated hearing impairment or conductive hearing loss. In otosclerosis patients, the auditory threshold curve displays a Carhart’s notch, which appears at tone frequencies of 1500 Hz. This Carhart’s notch is particularly pronounced in the presence of capsular otosclerosis. In patients with capsular otosclerosis, the bony labyrinth and its surrounding bones are affected.
There is no known procedure to prevent the bone remodeling process itself. Surgical treatment, during which the attempt is made to reestablish the hardened ossicular chain function, is usually recommended. This is usually performed by removing the stirrup and replacing it with a prosthesis (artificial stirrup). If the cochlea is affected, however, treatment does not have to be surgical; instead, the patient is given sodium fluoride for several months. For some otosclerosis patients, surgical treatment is not possible – making hearing aids the best possible solution to alleviate hearing impairment and ensure additional quality of life.