Auditory evoked potentials in epileptic patients

Auditory brain stem response (ABR) and middle latency response (MLR) were recorded in 49 epileptic patients. Responses were evoked and recorded at 90 dB nHL down to threshold. A statistically significant number of epileptic patients showed elevated ABR (30.1%) and MLR (40.7%) thresholds, even though their pure-tone audiograms showed normal hearing sensitivity. Threshold elevation was more frequent in subjects with grand mal epilepsy compared to subjects with temporal lobe epilepsy reflecting poorer response in the former subgroup. Furthermore, chronicity of illness was significantly related to the elevated ABR and MLR thresholds in grand mal patients in contrast to patients with temporal lobe epilepsy. On the other hand, the effect of antiepileptic drugs did not seem to be significantly related to the elevated thresholds in both subgroups. Threshold elevation was attributed to a disturbance in the neurotransmitters of the brain stem as well as other subcortical structures. The inhibitory effect of the efferent auditory pathway on the incoming neural signals was also suggested to explain such elevated thresholds.