Early Detection of Blast-Induced Hidden Hearing Loss in Military Personnel Using an Extended Audiological Battery

Background/Objectives: Military personnel are frequently exposed to high-risk acoustic trauma from blast waves. While macroscopic injuries like tympanic membrane perforation (TMP) are easily identified, subclinical microscopic damage, such as hidden hearing loss (HHL), often goes undetected by standard audiometry. This study investigates the auditory impacts of an accidental ammunition depot explosion, focusing on the diagnostic value of extended high-frequency (EHF) audiometry and objective electrophysiological measures in detecting early-stage blast-induced damage. Methods: This retrospective case series included eight military personnel involved in a 120 mm howitzer shell explosion at an ammunition depot. Subjects were categorized into direct blast exposure (n = 2) and indirect impact (n = 6). Audiological evaluations included otoscopy, standard pure-tone audiometry (0.25-8 kHz), EHF audiometry (9-14 kHz), auditory brainstem response (ABR), and distortion product otoacoustic emissions (DPOAEs). Results were compared to reference and control groups. Two patients with direct trauma underwent type I tympanoplasty to repair TMP. Results: Directly exposed personnel sustained near-total TMPs and significant mixed hearing loss. In contrast, the six indirectly impacted personnel exhibited "clinically normal" standard audiograms; however, their EHF thresholds at 9, 10, 12.5, and 14 kHz were significantly elevated compared to controls (p < 0.05). DPOAE amplitudes at 1, 1.5, and 10 kHz were significantly reduced in the blast group, indicating outer hair cell dysfunction. ABR showed a prolonged wave I latency with statistical significance (p = 0.014), but a decreased wave I amplitude was nonsignificant between groups; these findings are suggestive of possible cochlear synaptopathy, consistent with, but not diagnostic of, HHL. Conclusions: Blast exposure may produce both overt and subclinical auditory injury. Even in individuals with normal conventional audiograms, our preliminary findings suggest that EHF audiometry and otoacoustic emission testing show promise in identifying early cochlear dysfunction consistent with HHL. While further validation in larger cohorts is required to establish definitive diagnostic utility, these hypothesis-generating observations highlight the potential value of advanced audiologic assessments for the detection and monitoring of blast-related auditory injury in military personnel.