[15] 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
What additional symptom may present in otosclerosis?
- Speaking in a low volume
Why do patients with otosclerosis sometimes speak in a low volume?
Their voice appears loud to them
What will be seen on a Rinne and Weber’s test in most cases of otosclerosis?
Conductive hearing loss
What is the primary investigation of choice in otosclerosis?
Audiometry
What does audiometry typically show in otosclerosis?
Conductive hearing loss particularly at low-tones
What is a useful diagnostic investigation in otosclerosis?
CT scan
Why is CT scanning useful in otosclerosis?
It can rule out other differentials and improve targeting for surgery
What are the differentials for otosclerosis?
- Chronic suppurative otitis media
- Glue ear
- Damage to the ossicle from infection
- Congenital stapes fixation
- Post-infective tympanosclerosis
- Paget’s disease of bone
- Osteogenesis imperfecta
How can the management of otosclerosis be divided?
- Medical
- Surgical
How can otosclerosis be medically managed?
- Bilateral hearing aids
- Sodium fluoride to slow progression
How can otosclerosis be surgically managed?
Stapedectomy (removal of footplate) or stapedotomy (hole made in the footplate)
How can surgery help in otosclerosis?
Improves circulation of fluid within the cochlear canal
What are the potential complications of otosclerosis?
- Hearing loss of 50-60dB
Is deafness common in otosclerosis?
No
