PP318 - Role of Extended High Frequency Audiometry in Early Identification of Damage Caused by Noise Exposure

Abstract:
Noise exposure is one of the leading causes of hearing loss. Hearing thresholds in standard frequencies (0.25-8 kHz) may be clinically normal in the early stages of noise-induced damage, while thresholds in the extended high frequencies (EHFs) may offer a sensitive indicator of early noise-induced damage. In this presentation, we will discuss: (1) evidence from a meta-analysis that showed robust effects of noise exposure on EHF thresholds; and (2) our experimental work relating noise exposure and EHF thresholds in adults with normal audiograms. We will also discuss the clinical consequences of our findings for early detection of noise-induced subclinical damage.

Summary:
Rationale
Understanding the initial clinical signatures of noise-induced damage has high theoretical as well as clinical significance. Noise-induced hearing loss (NIHL) is one of the most prevalent and preventable causes of hearing impairment worldwide. In the US, estimates suggest that up to 24% adults may have NIHL. NIHL typically manifests as elevated hearing thresholds in a "notched" pattern typically at 4 kHz or occasionally at 3 or 6 kHz in the audiogram. A clinical audiogram, which assesses hearing thresholds from 0.25 to 8 kHz, may not sensitively detect early signs of noise-induced damage. Animal models suggest that the basal region of the cochlea is particularly vulnerable to noise exposure, regardless of the frequency content of the noise. This raises the possibility that extended high frequency hearing (EHF; > 9-20 kHz) hearing could serve as an early marker of NIHL. In the early stages of NIHL, the clinical audiogram may appear normal, while the EHF region could be impacted by noise exposure. The present study evaluated the relationship between noise exposure and EHF hearing in individuals with normal audiograms, in an attempt to detect subclinical hearing damage.

Design
We applied a two-pronged approach. (1) A systematic review and meta-analysis were conducted to quantify the association between noise exposure and EHF thresholds. (2) Cross-sectional data were collected from young normal hearing adults (N = 30, mean age = 21.7 years). The experimental protocol included: (i) a comprehensive audiological assessment including standard pure tone audiometry (0.25-8 kHz) and extended high frequency audiometry (10, 12.5, and 16 kHz); (ii) quantification of lifetime noise exposure via the Noise Exposure Structured Interview (NESI). The effect of age, sex, NESI score, hearing thresholds at standard frequencies, and EHFs were examined using linear mixed-effects models.

Results
The systematic review of the literature revealed elevated hearing thresholds in certain EHFs in 20 out of 28 studies. Meta-analysis showed a significant effect of noise exposure on hearing thresholds for 9-16 kHz. The effect size ranged from medium (9, 11.2, and 12.5 kHz) to large (12, 14, and 16 kHz), providing robust evidence for the association. Preliminary analysis from our cross-sectional study showed a significant positive correlation between NESI score and EHF thresholds, particularly at 12.5 kHz (r=0.62, p < 0.01).

Conclusions
Overall, evidence from both metanalysis and current cross-sectional data suggest that noise exposure is significantly associated with elevated EHF hearing thresholds in adults with normal audiograms, highlighting the subclinical damage from noise exposure. It also suggests that hearing damage in the early stages occur for EHFs, even before standard-frequency hearing loss is clinically detectable. In addition, we will discuss the frequency specific effects of noise exposure and whether EHF loss precedes a 4-kHz audiometric notch.

These findings underscore the value of incorporating EHF audiometry into routine hearing assessments for noise-exposed individuals. By detecting subclinical damage, clinicians can intervene earlier, potentially preventing more severe and widespread hearing loss. We will also discuss the need for longitudinal designs to elucidate the progression of noise-induced hearing damage.

Brief Summary of Clinical Takeaways:
The clinical takeaway for this session is the importance of including extended high-frequency audiometry in regular hearing evaluations for individuals exposed to noise. This approach allows for the early detection of subclinical hearing damage, facilitating earlier intervention and potentially preventing more significant and widespread hearing loss.

Assumptions
Attendees should have understanding of normal hearing mechanisms, hearing loss, and the effects of noise exposure on hearing. They should also be aware of current practices, for early identification of noise-induced hearing damage.