ABSTRACT
A common auditory complaint of multiple sclerosis patients, is misunderstanding speech in the presence of background noise. Evidence from animal and human studies has suggested that the medial olivocochlear bundle may play an important role in hearing noise. The medial olivocochlear bundle function can be evaluated by the suppression effect of transient otoacoustic emission in response to contralateral acoustic stimulation. The present study was conducted to investigate the suppression effect of transient otoacoustic emission in multiple sclerosis patients. This analytical case-control study was conducted on 34 multiple sclerosis patients [24 female, 10 male], aged 20-50 years and 34 controls matched for age and gender in Faculty of Rehabilitation, Tehran University of Medical Sciences in 2006. All cases were selected in simple random manner. The suppression effect of transient otoacoustic emission was evaluated by comparing the transient otoacoustic emission levels with and without contralateral acoustic stimulation. Data were analyzed using SPSS software and independent T- test. There was no significant difference in transient otoacoustic emission levels of two groups, but a significantly reduced suppression effect of transient otoacoustic emission was found in multiple sclerosis patients, in compare with the controls. Outer hair cells activity in multiple sclerosis patients was normal but these patients presented low activity of the medial olivocochlear bundle system which could affect their ability to hear in the presence of background noise