On the use of click-evoked electric brainstem responses in audiological diagnosis. III. Latencies in cochlear hearing loss.

The basis for the use of click-evoked BSER in neurotologic differential diagnosis would seem to be its sensitivity to retrocochlear but relative resistivity to cochlear lesions. The present study was performed in order to investigate the presumed robustness of BSER in cochlear hearing loss by recording BSER in 110 consecutive cochlear ears with click thresholds not in excess of 60 dB HL. There were eleven ears with rising, twenty-two ears with flat, and 77 ears with sloping audiograms. Click intensities were 80 dB HL and 60 dB SL, and the BSERs were observed for replicability and latencies of waves I, III and V, as well as for I-V and III-V interpeak intervals. Wave V latency increments (relative to normal values) were related to hearing thresholds at 4 kHz. Wave V was identifiable in all of the ears at 80 dB HL and/or 60 dB SL, whereas waves I and III often failed to appear at 80 dB HL and occasionally at 60 dB SL. At 80 dB HL click level, the wave V latency increment was related to the 4 kHz hearing loss (statistically significant at level 0.05 in the HF loss group), increasing by approximately 0.1 ms for each 10 dB, starting at 30 dB HL. Increasing click intensity to 60 dB SL tended to bring waves I and III into appearance and to offset the V latency increase (even inverting it in highly recruiting flat loss ears). Interpeak intervals were not significantly affected by cochlear hearing loss. Unfiltered alternating clicks were used after two initial experiments had shown that nothing would be gained in this study from using filtered clicks or uniphase unfiltered clicks.