A 55-year-old man with progressive unilateral sensorineural hearing loss undergoes a tone decay test. Threshold shifts by more than 30 dB during continuous presentation of a sustained tone at suprathreshold level. This result is most suggestive of which lesion?
- A Retrocochlear lesion such as vestibular schwannoma ✓
- B Cochlear hair cell loss from noise exposure
- C Ossicular chain discontinuity
- D Endolymphatic hydrops
Correct answer: A. Retrocochlear lesion such as vestibular schwannoma
Explanation
The tone decay test measures auditory adaptation to a continuous suprathreshold tone. Decay greater than about 30 dB is pathological and localizes to the eighth nerve, classically a vestibular schwannoma at the cerebellopontine angle. Mild decay up to 20 to 25 dB can be seen in cochlear lesions, but marked decay is a retrocochlear sign. Conductive lesions such as ossicular discontinuity do not produce abnormal neural adaptation.
Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.