2018 Volume 61 Issue 2 Pages 145-153
New insights from animal studies suggest that the most vulnerable elements in the inner ear are the synaptic connections between the inner hair cells and the cochlear neurons. We show a case with a normal pure-tone audiogram, poor word recognition score, and reduction of the ABR amplitude, suggesting the validity of measuring cochlear synaptopathy. ABR wave I is useful in animal models. However, the amplitude of ABR wave I shows both high inter-subject and intra-subject variability in humans, so that its clinical usefulness is restricted. In this study, the intra-subject variability of the ABR amplitude was investigated. The variance of the background noise was practically negligible, allowing estimation of the variance of the evoked potential recorded in response to stimulus levels of over 40dB nHL. In a normal-hearing subject, the standard deviation of the wave I amplitude tended to decrease as the sample size increased from 500 to 2000 repetitions. Assuming that the 40dB nHL for normal hearing was equivalent to the threshold for hearing loss of 30dB SL, the wave I amplitude in ears with hearing loss was significantly higher than that in ears with normal hearing. The coefficient of variation (CV) of the wave I amplitude in ears with hearing loss was significantly smaller than that in ears with normal hearing.
