Ken W. Grant1, Sandeep A. Phatak1,2, Lina R. Kubli3, Kimberly A. Jenkins1, Jennifer R. Myers4, Douglas S. Brungart1
1 Walter Reed National Military Medical Center, Audiology and Speech Pathology Center, Bethesda, MD, USA; 2 The Geneva Foundation, Tacoma, WA, USA; 3 The U.S. Dept. of Veterans Affairs, RR&D Sensory Systems and Communication Disorders Program, Washington DC, USA; 4 Neurotrack Biotechnology, Redwood City, California
Background: Military audiologists routinely see Service members (SMs) with clinically normal-hearing thresholds (NHT) who present with hearing difficulties not consistent with their audiogram. Many of these SMs also report being exposed to one or more blasts during deployments. The purpose of this study was to investigate sensory and cognitive factors that might lead to such functional hearing deficits, and to provide insight into potential rehabilitative strategies.
Methods: Two groups of blast-exposed SMs – those with or without suspected FHCD – were evaluated. FHCD was identified using a rapid screener consisting of two auditory tests and a 6-question survey. Once enrolled, subjects were further evaluated using a battery of behavioral, electrophysiological, and cognitive tests. These tests were selected to provide insight into the likely factors contributing to FHCD. Results for blast-exposed SMs were compared with an age-matched control group of SMs with audiometric thresholds ≤ 20 dB HL, no history of blast-exposure, and no evidence of FHCD.
Results: A 3-way comparison (i.e., age-matched controls, and blast-exposed SMs with or without FHCD) showed that SMs with FHCD performed significantly worse than control subjects on behavioral and electrophysiological metrics sensitive to sensory deficits in auditory processing. There was also evidence of some cognitive deficits, especially on tests of speed of language-processing. By comparison, SMs without FHCD performed more like the control group.
Conclusions: Blast-exposed SMs with clinically normal audiograms and evidence of FHCD appear to have poorer peripheral auditory processing and a poorer internal signal-to-noise ratio when compared with control subjects or with blast-exposed SMs without FHCD. Results suggest that blast-exposed SMs with NHT and FHCD are likely to have sensory processing deficits, findings consistent with the growing practice to prescribe low-gain hearing aids for this population.