[Evoked otoacoustic emissions in noise-induced hearing loss]

The Authors evaluated patterns of click-evoked otoacoustic emissions (EOE) in a group of 184 patients exposed to noise in their working environment. The aim of the study was to detect changes in EOE patterns in this group compared to the EOE of healthy subjects. The clinical history of each subject was recorded and otoscopy, pure tone audiogram and impedance tests (tympanometry, stapedial reflex threshold) were carried out in all patients. Noise-induced hearing loss found in 97 patients, unilateral sensorineural hearing loss in 17, other hearing disorders in 24 and normal auditory threshold in 46. EOE recording was carried out in the group of patients with noise-induced hearing loss (97), in the group with normal threshold (46) and in a control group of 15 healthy subjects. EOE recording was obtained using the ILO 88 Otodynamic Analyzer. We introduce a probe into the external ear canal using a non-linear click stimulus (intensity at approximately 85 dB spl) at a 20/sec. rate with a 20 msec. window. Normal EOE were found in the control group. Abnormal EOE were found in 79 cases (81%) of the noise-induced hearing loss group, and in 22 (48%) of the normal threshold group. These data show that noise-exposed subjects have alterations of EOE such as threshold shift missing frequency bands, even in absence of an auditory threshold shift. When EOE were present, the frequency spectrum often showed lack of emissions at high frequencies. This study confirms that cochlear exposure to noise may produce significant alterations of EOE and that this test may be considered highly sensitive in detecting early cochlear damage in chronic acoustic trauma. Therefore, EOE may be used in screening and follow-up of high risk populations such as noise-exposed subjects.