On pure tone audiometry, a patient demonstrates air conduction thresholds of 50 dB at all frequencies with bone conduction thresholds of 20 dB. The Carhart notch (dip at 2000 Hz on bone conduction) is present. What is the diagnosis?
- A Otosclerosis causing conductive hearing loss ✓
- B Sensorineural hearing loss due to noise damage
- C Cochlear dead regions
- D Auditory neuropathy spectrum disorder
Correct answer: A. Otosclerosis causing conductive hearing loss
Explanation
The Carhart notch is a bone conduction dip of approximately 5 dB at 500 Hz, 10 dB at 1000 Hz, 15 dB at 2000 Hz, and 5 dB at 4000 Hz seen in otosclerosis. It is a mechanical artifact from stapes fixation and not a true sensorineural loss — it disappears after successful stapedectomy. The 30 dB air-bone gap along with Carhart notch is pathognomonic of otosclerosis. Noise-induced SNHL would show a 4000 Hz notch in air conduction.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.