Usefulness of auditory brainstem responses at high stimulus rates in the diagnosis of acoustic neuroma.

The effects of the stimulus rate on the auditory brainstem responses (ABRs) of acoustic neuroma (AN) patients were studied. Ninety-decibel click stimuli at a normal hearing level were delivered at stimulus rates of 9.5, 20, 40 and 90 Hz, and ABRs were recorded of 40 AN patients (40 ears) at each stimulus rate. Subjects with normal hearing (42 ears) and patients with sensorineural hearing loss (30 ears) were also studied to obtain normative data. The following two parameters were examined: the interpeak latency difference between wave I and wave V (IPL I-V) at each stimulus rate, and the increase in IPL I-V (delta IPL I-V) when the stimulus rate was increased from 9.5 Hz. AN patients showed significantly larger values for both parameters at all stimulus rates compared to those of the control groups. Among 6 AN patients with normal ABRs at 9.5 Hz, 5 showed abnormal IPL I-V or abnormal delta IPL I-V at 90 Hz, when the upper normal limits of both parameters were defined as the mean plus 2 SD of the group with normal hearing. These results suggest that recording ABR at high stimulus rates provides valuable information for detecting AN patients with normal ABRs.