Audiological characteristics of blast-induced hearing loss and tinnitus: unique outcomes in select cases

Auditory perceptual, electroacoustic, and questionnaire-based outcomes were examined in twenty-one adults following blast overpressures. Pure-tone thresholds, monosyllabic word recognition in quiet and in noise, wide band middle ear power reflectance, distortion product otoacoustic emissions, loudness perception, tinnitus-loudness levels, and questionnaire-based assessment of self-perceived tinnitus handicap were evaluated. Audiometric data were characterized by normal pure-tone thresholds, noise-notched profiles, downward sloping, and flat audiometric losses. Within these data, two unique and novel outcomes were identified: (1) subgroups of individuals having normal pure-tone thresholds with distinctly abnormal DPOAE microstructure and (2) subgroups of individuals having reverse slope audiograms with and without concomitant high-frequency sensorineural hearing loss. Results from the Tinnitus Handicap Questionnaire were uncorrelated with any of the audiometric measures. Loudness hyperacusis was absent and cochlear synaptopathy was not convincingly observed in any of the enrollees. The assessment of individual differences was a key determinant that allowed for identification of these unique audiologic outcomes. Notably, these effects would have been missed if "averaged" results were the principal data analysis strategy used across subjects.