Otosclerosis is a metabolic bone disease that causes hearing loss. It affects the ossicles and the temporal bone. In otosclerosis normal bone is absorbed and replaced by abnormal sclerotic bone.
Otosclerosis is present in 10% of the population but only 1% will develop hearing loss. The development of hearing loss depends on the location of the otosclerotic focus. If the ossicles are involved, especially when the otosclerotic bone fixates the stapes a conductive hearing loss is seen. In some cases the cochlea can be involved and patients with cochlear otosclerosis will present with mixed or sensorineural hearing loss.
Otosclerosis is a genetic disorder, transmitted in an autosomal dominant way with invariable penetrance. The trigger that sets of the development in these patients is unknown. Hormonal, metabolic, infectious (measles), vascular and, autoimmune causes have been implicated. A positive family history can be found in up to 70% of cases.
Females are twice as likely to suffer from clinical otosclerosis than males. Generally hearing loss presents between 15 and 45 years of age. In females it is most commonly seen in the 20 – 30 year age where pregnancy is responsible for rapid progression in 15% of cases. It is rare in childhood. Both ears are affected in 80% of patients.
Patients usually present with slow progressive hearing loss that may be asymmetric. Tinnitus occurs in 75% and dizziness and vertigo in 25% of patients.
After a clinical examination, hearing tests and acoustic reflexes are ordered that will confirm a hearing loss. A high resolution computed tomography (CT) scan of the temporal bone might help to confirm an otosclerotic focus. It may also help to exclude other conditions such as a superior canal dehiscence (SCD) that may mimic it.
The hearing loss due to otosclerosis can be managed with hearing amplification, oral sodium fluoride, surgery or a combination. The most common procedure performed nowadays is a stapedotomy. A small hole is created in the footplate of the stapes where after prosthesis is placed from the incus into the hole. This reestablishes the conduction of sound.