6.1 Definition

• An autosomal dominant disease of incomplete penetrance affecting bone derived from the otic capsule in which mature lamellar bone is replaced by woven bone of greater cellularity and vascularity

6.2 Pathology

• Aetiology

Genetics: autosomal dominant with incomplete penetrance

Autoimmune: there may be an autoimmune component to the aetiology (autoimmunity to type II collagen)

Hormonal: oestrogens stimulate osteoclastic activity; disease noted to progress with pregnancy/menopause

Viral: measles infection in particular may have a secondary role in those with a genetic predisposition

• Confined to human temporal bone derived from otic capsule; the new woven bone has increased cellularity and vascularity alongside fibrous replacement and sclerosis; alternating phases of bone resorption and formation

• During embryonic ossification of cochlea the area anterior to oval window remains cartilaginous before degenerating to simple fibrous tissue and forming fissula ante fenestram, which becomes the most common site for otosclerotic focus

• Vascular connective tissue replaced by neo-osteogenesis

6.3 Clinical Presentation

6.3.1 History

• M:F 1:2, middle-aged; positive family history in 50%; effect

• Gradual onset of conductive hearing loss (CHL); in time ~10% develop sensorineural hearing loss (SNHL)

• Active progression during pregnancy

• Paracusis of Willis—speech perceived better in a noisy background because better discrimination when stimulus is raised above normal conversational level

• Bilateral in ~80%

• Tinnitus common

• Vertigo can occur with an otosclerotic focus in labyrinth

• May coexist with Ménière disease (relative contraindication to stapedectomy)

6.3.2 Examination

• tympanic membrane (TM) usually unremarkable

• Schwartze sign—vascular or “flamingo” flush over the promontory

• CHL ± SNHL

• Tuning forks: usually Rinne–ve (256 Hz flips at ~15–20 dB air–bone gap (ABG), 512 Hz at ~25 dB, 1024 Hz at ~30–35 dB)

6.3.3 Audiometry

• pure tone audiogram:

Progressive conductive hearing loss (HL)

When cochlea involved, SNHL added component