Clinical interpretation of brainstem evoked response audiometry abnormalities in cochlear pathology

This investigation involved 45 patients with sensorineural hearing loss (SNHL): 24 with Meniere's disease, 18 with acoustic trauma, and 3 with SNHL due to ototoxic drugs. They all underwent pure tone audiometry and standard brainstem evoked response audiometry (BERA). In patients without wave I in auditory brainstem response, electrocochelography (ECochG) was performed. The findings are presented showing that cochlear lesions (beside threshold elevation) cause latency prolongation of wave I, III and V relative to normal latencies at the actual click hearing level. At high stimulation levels, this effect is almost completely compensated for by the fact that cochlear recruiting ears exhibit steeper latency-intensity curves than do normal ears. But, at the same time this pathology does not cause latency prolongation of central conduction time (CCT). Beside this, cochlear lesions will cause, in some cases, deterioration of replicability (poor waveform resolution) of waves preceding wave V. In such cases, the authors strongly recommend electrocochleography (ECochG) to make wave I visible, because they think that it is the best way to verify the diagnosis of cochlear lesion using BERA.