[Otoacoustic distortion products in sensorineural hearing loss in the cochlea]

The purpose of the present work was to assess distortion-product otoacoustic emissions (DPOAE) in cochlear hearing loss and in its various morphologies. A total of 19 patients (30 ears) were selected for the study. They showed various pictures of neurosensorial hearing loss which were localized within the frequency range normally examined during audiometric tonal threshold testing. The DPOAEs were recorded using a Bray and Kemp ILO 92 instrument. The DPOAEs of several frequencies (750,1000,1500,2000,3000,4000 and 6000 Hz) were examined using an f2 tone of 696, 1001, 1587, 2002, 3147, 4004 and 6348 Hz, respectively. The results were as follows: a) At certain frequencies the overlap between hearing loss and the absence of, or reduction in, DPOAE amplitude was virtually total. b) There was a modest correlation between the degree of hearing loss and decrease in, or absence of, DPOAEs although there was a spectrum of intermediate hearing losses where the DPOAEs varied widely from one individual to another (this spectrum ranged from 10 to 45 dB HL on the audiometric tonal test). c) The absence of DPOAEs at 750 Hz is unable to predict hearing loss for this frequency as, at this frequency, there can be a lack of DPOAEs even when the 750 Hz audiometric threshold level is normal. Finally, what emerged from this study was that DPOAEs prove quite useful to complement the study of auditory brainstem responses (ABR), now universally accepted as the means for early diagnosis of hearing loss in children. In fact, ABRs provide precise data regarding a frequency field which is socially less important in terms of verbal communication and the development of spoken language. It is, however, unable to explore individual frequencies.