[Effects of stimulus rate on the ABR of acoustic tumor patients].

The effect of stimulus rate on the ABR of acoustic tumor (AT) patients was studied. We delivered 90 dB nHL click stimuli to 23 AT patients at stimulus rates of 9.5 Hz, 20 Hz, 40 Hz and 90 Hz, and recorded the ABR at each rate. Normal hearing subjects (42 ears) and sensorineural hearing loss patients (30 ears) were also studied for 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. The values of both parameters were statistically larger in AT patients at all stimulus rates than in the normal and sensorineural hearing loss groups. When the upper normal limit of both parameters was defined as the mean plus 2SD of the normal hearing group, 4 of the 5 AT patients with a normal ABR at 9.5 Hz, had abnormal IPL I-V or abnormal delta IPL I-V at 90 Hz. These results suggest that recording ABR at high stimulus rates is effective in detecting acoustic tumors in patients with a normal ABR.