Is Noise Exposure Associated With Impaired Extended High Frequency Hearing Despite a Normal Audiogram? A Systematic Review and Meta-Analysis.

Understanding the initial signature of noise-induced auditory damage remains a significant priority. Animal models suggest the cochlear base is particularly vulnerable to noise, raising the possibility that early-stage noise exposure could be linked to basal cochlear dysfunction, even when thresholds at 0.25-8 kHz are normal. To investigate this in humans, we conducted a meta-analysis following a systematic review, examining the association between noise exposure and hearing in frequencies from 9 to 20 kHz as a marker for basal cochlear dysfunction. Systematic review and meta-analysis followed PRISMA guidelines and the PICOS framework. Studies on noise exposure and hearing in the 9 to 20 kHz region in adults with clinically normal audiograms were included by searching five electronic databases (e.g., PubMed). Cohorts from 30 studies, comprising approximately 2,500 participants, were systematically reviewed. Meta-analysis was conducted on 23 studies using a random-effects model for occupational and recreational noise exposure. Analysis showed a significant positive association between occupational noise and hearing thresholds, with medium effect sizes at 9 and 11.2 kHz and large effect sizes at 10, 12, 14, and 16 kHz. However, the association with recreational noise was less consistent, with significant effects only at 12, 12.5, and 16 kHz. Egger's test indicated some publication bias, specifically at 10 kHz. Findings suggest thresholds above 8 kHz may indicate early noise exposure effects, even when lower-frequency (≤8 kHz) thresholds remain normal. Longitudinal studies incorporating noise dosimetry are crucial to establish causality and further support the clinical utility of extended high-frequency testing.