LOW DPOAES WITH NORMAL AUDIOGRAMS AND THE RISK OF EARLY HEARING LOSS AT NOISE EXPOSURE : PREDICTIVE VALUE OF AN OTOACOUSTIC VULNERABILITY INDEX

Job A(1), Raynal M (2), Kossowski M (2).

(1) CRSSA centre de recherches du service de santé des armées, France; (2) Hopital d'instruction des Armées de Percy, France.

Background : It is unknown whether low distortion product otoacoustic emissions (DPOAEs) are risk markers for subsequent early hearing loss in normal hearing ears exposed to noise.

Objective: To identify at risk subjects for early hearing loss in a normal hearing population using an index of abnormal DPOAEs (IaDPOAE) to estimate ear vulnerability to noise

Study Design : A longitudinal study.

Methods: The study population consisted of pilots 20-40 years old. Data collection consisted of tonal audiograms, DPOAEs measurements completed by the IaDPOAE calculation and a clinical questionnaire. The cut-off value of 15% for the IaDPOAE gave the best sensitivity and specificity to part normal hearing ears from impaired hearing ears (n=550). We could re-tested 219 of 340 normal ears (all frequencies = 10dB HL) after 3 years and we observed the occurrence of impaired ears (at least one frequency > 25 dB HL), depending if IaDPOAE was initially low (<15%) or high (>15%).

Results : In initially normal hearing ears, occurrence of impaired hearing, 3 years later was, in the high IaDPOAE group compared to  low IaDPOAE group, 21% and 8%,  respectively (p<0.012). Early hearing loss in normal ears with IaDPOAE > 15% were associated with a relative risk of 2.9 (95% CI, 1.24 to 6.58)

Conclusion: Low DPOAEs espacially IaDPOAE >15% is a risk marker for early hearing loss. It predicts a vulnerability before the alteration of audiograms. This study emphasised the high interest of DPOAE measurements in noise exposure prevention policies.

E-mail: ajob.crssa@gmail.com