Speech audiometry in a 55-year-old man with asymmetric sensorineural loss gives a phonetically balanced word score of 64% at 40 dB sensation level, falling to 26% at 80 dB sensation level. The rollover index is:

• A 0.18, normal
• B 0.38, borderline
• C 0.59, abnormal, suggesting retrocochlear lesion ✓
• D 0.85, abnormal, suggesting cochlear lesion

Explanation

Rollover index equals (maximum score minus minimum score) divided by maximum score: (64 minus 26) divided by 64 equals 0.59. An index above 0.45 is abnormal and indicates disproportionate deterioration of word recognition as intensity rises, a hallmark of retrocochlear lesions such as vestibular schwannoma. Cochlear losses may show mild rollover but generally remain below this cutoff, and conductive losses show none because scores improve steadily with intensity.

Reference: Glasscock-Shambaugh, Surgery of the Ear, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.