Otosclerosis Flashcards
What is otosclerosis?
A genetically mediated metabolic dysplasia affecting the bony tissue of the otic capsule and ossicles
What is the otic capsule?
The skeletal elements enclosing the inner ear mechanism
What is the pathology in otosclerosis?
Increased bone turnover leading to sclerosis and failure of the sound conduction mechanism
Why is there failure of the sound conduction mechanism in otosclerosis?
Due to ankylosis (fusion) of the stapes footplate in the fenestra ovalis of the cochlea
What does ankylosis of the stapes footplate in the oval window lead to?
Slowly progressive conductive hearing impairment
What can happen to the conductive hearing impairment in some cases of otosclerosis?
Progresses to a mixed hearing loss
Why can otosclerosis progress to a mixed hearing loss?
The bony tissue can extend into the cochlea itself
What is the inheritance of otosclerosis?
Autosomal dominant with variable penetrance
What does penetrance mean in terms of genetics?
Whether those who have the genotype display the phenotype
e.g. not all those with otosclerosis genotype will have the ‘condition’ (variable penetrance)
What is thought to be critical in the phenotypic activation of otosclerosis?
Environmental factors
What environmental factors are thought to play a role in the activation of otosclerosis?
- Oestrogens
- Fluoride
- Viral infections such as measles
What are the risk factors for developing otosclerosis?
- White or asian
- Female
- Age 15 - 35
- Family history
What are the main symptoms of otosclerosis?
- Progressive hearing loss
- Tinnitus
In what percentage of cases of otosclerosis is hearing loss bilateral?
70%
Are vestibular symptoms present in most cases of otosclerosis?
No
