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Abstract
Summary Summary Cochlear hearing loss is often associated with damage to the hair cells within the cochlea. Sometimes, the inner hair cells IHCs at certain places along the basilar membrane may be completely non-functioning or even missing, which means that there is no transduction of basilar membrane vibration at these places. In addition, the auditory neurons associated with certain places may be non-functioning or degenerated, which again means that information about basilar membrane vibration at those places is not transmitted to the brain. Places where there are no functioning IHCs and/or neurons are referred to as ”dead regions”(Moore, 2001, 2004). Dead regions can be detected clinically using threshold equalizing noise (TEN) test.This study was designed to study the prevalence of dead regions in the cochlea in hearing impaired patients with different audiometric configurations and to correlate the dead region with speech discrimination scores. It was carried on 80 subjects, with age ranging from 18-50 years, divided into control and study group, the control group: comprised 30 subjects with normal hearing sensitivity. The study group : comprised 50 patients suffering from sensorineural hearing loss with no restrictions regarding audiometric level or configuration, This group was further subdivided according to the results of TEN test into 2
subgroups: subgroup A: patients with negative results of TEN test,subgroup B : represents patients with positive TEN test results. Equipments used in this study were two channel audiometer, sound-treated booth, Immittancemeter, DVD ,Compact disc (CD)Summary containing TEN (HL) test (Moore et al, 2003), Evoked potential system, smart Ep version 1.2Xwith soft ware Intelligent Hearing System Program.All subjects in this study were submitted to full history taking, Otological examination, basic audiological evaluation, TEN (HL) test for each ear, click auditory Brain stem evoked potentials.39 patients in the study group gave negative results of TEN
test, 11patients gave positive results of TEN test Prevalence of dead regions of the cochlea in this study was 22%, Dead regions in the cochlea were more common in patients with sloping, long standing hearing loss and in high frequencies, dead regions can be unilateral or bilateral, can be
single or multiple. Dead regions are not found in flat sensorineural hearing loss and mild degree of hearing loss There was no significant difference between the study subgroups in the speech discrimination scores in quiet and latency of wave I of click ABR. Results from comparison of thresholds generated from standard pure-tone audiometry and thresholds generated from the TEN test CD suggest that the thresholds are similar.