[Distortion product otoacoustic emissions (DPOAE) in chronic noise-induced hearing loss--recommendations for expert assessment].

The German guidelines for evaluation of chronic noise-induced hearing loss (NHL) require two special auditory tests besides pure tone and speech audiometry tests as proof of damage to the organum spirale. This requirement is the subject of controversy because of the subjective nature of the tests as well as the secondary ascending degeneration of neurons in cases of long-term NIHL. The application of otoacoustic emissions (OAE) could be a new starting point, independent of recruitment. DPOAE are preferable to TEOAE because they are frequency specific. For this reason, we carried out measurements of DPOAE in addition to the required tests on 33 patients (= 66 ears). The results are collected in four groups according to the pure-tone audiogram: a) slight b) typical, c) severe, d) no NIHL. The respective DP-Gram curves had typical features similar to the course of the pure-tone audiogram. The following conclusions are possible: a) in the frequency range up to 1 kHz, ambient noise often causes interference to the DP, b) in the frequency range from 1 kHz to the frequency of the steep pure-tone threshold decay clear DP amplitudes are seen, c) from a inner ear caused hearing loss of appr. 50 dB no DP are detectable, d) DP amplitudes are approximately inversely proportional to hearing loss, e) in severe NIHL (group C) or even slight conductive hearing loss (group D) no DP are found. Based on these results, we recommend including DPOAE as a further differential diagnostic test in the evaluation of NIHL.(ABSTRACT TRUNCATED AT 250 WORDS)