In pure tone audiometry, the difference between the air-conduction threshold and the bone-conduction threshold (air-bone gap) in an individual with otosclerosis is typically seen in which frequency range first?

• A High frequencies (4000–8000 Hz) predominantly
• B Mid frequencies (1000–2000 Hz) with flat loss
• C Low frequencies (250–500 Hz) predominantly ✓
• D All frequencies equally from the outset

Explanation

In early otosclerosis (fenestral type), the conductive hearing loss appears first and is most prominent at low frequencies (250–500 Hz). This is because fixation of the stapes footplate impairs the low-frequency resonance of the ossicular chain disproportionately, while high-frequency transmission relies more on inertia and is relatively preserved initially. As disease progresses, the air-bone gap widens across all frequencies. The Carhart notch (dip in bone conduction at 2000 Hz) is a mechanical artefact, not true sensorineural loss.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.