Early Detection of Noise Induced Hearing Loss by Extended High Frequency Audiometery

Surrounding noise, especially in industrial environments, is one of the most common etiologic factors of sensory-neural hearing loss (SNHL), which is not curable, but preventable. By industrialization of communities, the prevalence of the disease and its unfavorable socioeconomic outcome is growing up. Since the preventable defect, early diagnosis has the utmost importance. In recent years, the role of extended high frequency audiometry (EHFA) as a sensitive diagnostic tool for noise induced hearing loss has received much attention. This study deals with the role of EHFA in early diagnosis of this disorder. This was a retrospective cohort study during 2003-4 in Isfahan, Iran. A total number of 30 male labors, aged 20-50 years working in a noisy industrial environment, were compared with an equal number of controls with normal conventional audiometry, and no risk factor for other causes of SNHL according to their history and otoscopic examination. All 60 individuals underwent both types of conventional and extended high-frequency audiometry. Data were analyzed with SPSS software using t-test, paired t-test and correlation tests of Pearson and Spearman. There was no difference between the right and left ears. The exposed subjects had significantly worse hearing than the non exposed group, at all tested frequencies (especially at 16 KHz). The age effect was notable in both groups. The correlation between high frequency threshold and duration of noise-exposure was significant only at 16, 18 and 20 KHz. The higher mean frequency threshold of the cases was predictable; the normal findings of conventional audiometry, reveal that EHFA can be useful in early diagnosis of acoustic injuries.