Hearing Loss Asymmetry due to Chronic Occupational Noise Exposure.

OBJECTIVE: To determine whether occupational noise exposure causes symmetrical or asymmetrical hearing loss. STUDY DESIGN: Retrospective Case Series. SETTING: Otorhinolaryngology Specialist Centre. PATIENTS: Seven hundred forty-four reports for occupational noise-induced hearing loss (NIHL) compensation were analyzed. Subjects with at least 40% of their total hearing loss due to occupational NIHL were included. Claimants with any confounding factor that could cause asymmetric hearing loss such as history of shooting, head, or ear trauma were excluded. With the strict inclusion criteria, 83 subjects were included in the study. Claimants with ≥40%, ≥60%, and ≥80% occupational NIHL of their total hearing loss were compared. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The left ear hearing threshold compared with the right ear hearing threshold (dB) at the frequencies 0.5 to 8 kHz. RESULTS: In the total group, the left ear hearing threshold was statistically significantly higher compared with the right ear at 3 kHz (2.41 dB). In the subgroups ≥60% and ≥80% occupational NIHL of total hearing loss, the left ear hearing threshold was statistically significant higher compared with the right ear at 3 kHz, respectively, 3.81 dB and 5.53 dB and 4 kHz, respectively, 2.86 dB and 5.53 dB. An asymmetry of more than 10 dB at 3 and 4 kHz was observed in 39% and 30% of the subjects respectively. In these cases, the vast majority had more pronounced hearing loss in the left ear. CONCLUSION: Findings of this study further indicate that the left ear is more susceptible to noise exposure compared with the right ear.