Makindo Medical Notes

Otosclerosis 👂: Abnormal bone remodelling of the otic capsule, particularly around the stapes footplate, leading to progressive conductive hearing loss. It is a fairly common cause of hearing loss in young adults. Carhart’s notch: a dip at 2 kHz on bone conduction audiogram — classic for otosclerosis, first described by Raymond Carhart in 1950.

About

• Common cause of gradual, progressive hearing loss in young adults.
• Onset typically in 20s–40s; may worsen during pregnancy.

Aetiology

• Strong genetic component — autosomal dominant with incomplete penetrance.
• Infectious link suggested (e.g. measles virus).
• Possible autoimmune contributions.
• Twice as common in women.

Pathophysiology

• The stapes (innermost ossicle) normally vibrates freely in the oval window, transmitting sound into the cochlea.
• In otosclerosis → abnormal bone formation fuses the stapes to the oval window.
• This impairs sound transmission → conductive hearing loss.
• In some cases, cochlear involvement occurs → mixed or sensorineural loss.

Clinical Features

• Hearing loss — progressive, often bilateral, classically conductive.
• Tinnitus common.
• No pain or discharge (distinguishes from infection).
• Speech: patients often speak quietly (unlike other hearing loss).
• Otoscopy: normal, healthy-looking tympanic membrane.

Investigations

• Audiogram: conductive loss, with a dip at 2 kHz in bone conduction (Carhart’s notch).
• Tympanometry: usually normal (Type A curve).
• CT temporal bone if surgical planning or atypical presentation.

Management

• Medical: Sodium fluoride sometimes used (stabilises abnormal bone remodelling, evidence limited).
• Hearing aids: Effective for conductive deafness at all stages.
• Surgical:
  • Stapedectomy or stapedotomy with prosthetic stapes replacement — restores ossicular continuity.
  • Very high success rates but carries small risk of total hearing loss, vertigo, or taste disturbance (chorda tympani injury).

References

• Carhart R. “Clinical application of bone conduction audiometry.” Arch Otolaryngol 1950.
• ENT UK Otosclerosis patient information leaflets.

💡 Clinical Pearls

• Think otosclerosis in a young woman with progressive conductive loss and normal eardrum.
• Carhart’s notch at 2 kHz is highly exam-tested.
• Unlike chronic otitis media, there is no history of infection or tympanic membrane abnormality.