A 30-year-old woman presents with progressive bilateral conductive hearing loss. Audiometry shows bilateral low-frequency conductive loss with a Carhart's notch at 2000 Hz. Tympanometry shows Type As (stiff) curve. The most likely diagnosis and the underlying mechanism are:
- A Ossicular discontinuity — post-traumatic incudostapedial joint disruption
- B Otosclerosis — spongy vascular bone replacing the bony labyrinth around the oval window, fixing the stapes footplate ✓
- C Superior semicircular canal dehiscence — third window effect reducing cochlear impedance
- D Chronic otitis media with tympanosclerosis — calcium plaques fixing the ossicular chain
Correct answer: B. Otosclerosis — spongy vascular bone replacing the bony labyrinth around the oval window, fixing the stapes footplate
Explanation
Otosclerosis is a hereditary disorder of abnormal bone remodelling at the fissula ante fenestram (anterior to the oval window). Spongy (otospongiotic) bone replaces the normal enchondral bone, eventually fixing the stapes footplate and causing progressive low-frequency conductive hearing loss. The Carhart's notch (a dip in bone conduction at 2000 Hz that is mechanical not true SNHL) is pathognomonic. Tympanometry Type As (reduced compliance) confirms stapes fixation. Treatment is stapedectomy/stapedotomy.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.