Overall versus individual changes for otoacoustic emissions and audiometry in a noise-exposed cohort.

OBJECTIVE: For a noise-exposed group of workers, group-averaged and individual changes were compared for pure-tone audiometry, transient-evoked otoacoustic emissions (TEOAEs), and distortion product otoacoustic emissions (DPOAEs) in order to see if they exhibit the same pattern in time.

DESIGN: Baseline and 17-months follow-up hearing status was examined with pure-tone audiometry, TEOAEs, and DPOAEs.

STUDY SAMPLE: A total of 233 noise-exposed employees were measured, while 60 subjects from this group contributed to test-retest reliability measures.

RESULTS: Group-averaged changes and individual shifts followed similar patterns: decreases for audiometry at 6-8 kHz and DPOAE at 1.5 kHz, and enhancements for DPOAE at 3 kHz. TEOAEs showed an overall deterioration while both individual deteriorations and enhancements were larger than chance. DPOAE at 6 kHz showed the largest group-averaged change, while the number of individual shifts was not significant. There were no clear relations between changes in audiometry and changes in OAE.

CONCLUSION: Significant individual OAE changes do not necessarily follow the same pattern as the group-averaged results. This limits the applicability of OAE testing for the monitoring of individual subjects. Furthermore, hearing deterioration might manifest itself in a local enhancement of otoacoustic emissions and not only in the form of decreases in amplitude.