Tone decay testing in a 50-year-old man shows that a continuous 1000 Hz tone at his threshold level becomes inaudible, and the intensity must be raised by 35 dB above the initial threshold to maintain perception for 60 seconds. This degree of tone decay points to:
- A Retrocochlear lesion of the VIII nerve ✓
- B Cochlear hearing loss
- C Conductive hearing loss
- D Normal auditory adaptation
Correct answer: A. Retrocochlear lesion of the VIII nerve
Explanation
In tone decay testing, decay of 0 to 15 dB is normal, up to about 20 to 25 dB occurs in cochlear lesions, and decay exceeding 30 dB is characteristic of retrocochlear pathology such as vestibular schwannoma. Neural lesions show pathological auditory adaptation, meaning the ear cannot sustain perception of a continuous suprathreshold tone. D shift of 35 dB therefore localizes the lesion to the VIII nerve rather than the cochlea.
Reference: Dhingra, Diseases of Ear, Nose and Throat, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.