Acoustic trauma in soldiers: Pure-tone audiometry versus distortion product otoacoustic emissions as a tool for early detection

Background: Acoustic trauma is the sudden hearing loss that results following exposure to a single intense sound. Military environments inherently expose its personnel to very high levels of noise. Early detection of temporary or permanent hearing damage in soldiers following acoustic trauma and identification of their susceptibility to noise exposure is of utmost importance to better protect and prevent hearing deterioration. Conventionally, pure-tone audiometry (PTA) has been used as a screening method to detect hearing threshold shift following noise exposure. However, research now suggests distortion product otoacoustic emission (DPOAE) as a more sensitive tool to detect early changes in hearing thresholds following acoustic trauma. The aim of this study is to compare PTA and DPOAE for the early detection of acoustic trauma in soldiers. Methods: A prospective cohort multicentric study was conducted over a 2-year duration at 5 military hospitals on 1500 newly inducted recruits with no previous exposure to firing. After a thorough history taking and a comprehensive ENT examination, PTA and DPOAE tests were conducted at three intervals: before firing (initial evaluation), 2 h after firing (mid-evaluation), and 7 days after firing (final evaluation). The symptoms presented by the recruits were also analyzed. Statistical analysis between the two modalities of investigation to detect early acoustic trauma was done using Chi-square test. Results: Four hundred and eighty-seven recruits (36.07%) developed temporary threshold shifts and 103 (7.6%) had permanent threshold shifts. The most common symptom at mid-evaluation was tinnitus (501; 37.11%) while the least common symptom reported was isolated dizziness (10; 0.74%). At final evaluation, the most common symptom was found to be tinnitus (132; 9.77%). Conclusion: PTA and DPOAE can both be effectively used as a tool of measurement for the detection of early acoustic trauma, though being an objective test DPOAE has the advantage of eliminating subjective variation.