Vestibular function following blast injury

Abstract

To date, the war on terror has produced over 30,000 wounded military personnel with a large proportions of injuries attributed to blasts. Dizziness and imbalance are common complaints among the blast-injured population. The functional consequences to the inner ear vestibular system, following blast exposure have not been well characterized. Previous researchers have used small sample sizes, limited test batteries, and/or descriptive review of results. The present research consisted of two experiments. In the first experiment vestibular and ocular motor function in military personnel with primary blast injury was characterized to further develop our understanding of post-blast induced dizziness/imbalance. The hypothesis for experiment one was that 40 to 50% of those blast injured population would show evidence for peripheral vestibular deficits. A comprehensive test battery including vestibular assessment, auditory evoked potentials, and ocular motor testing was utilized. In experiment one, it was demonstrated that 11.6% of the blast injured population showed evidence of peripheral vestibular abnormality. Fifty-one percent of the cohort showed evidence for ocular motor abnormalities with prolonged saccadic latencies being the most common ocular motor abnormality. The ocular motor results are consistent with central pathology. Subjective scales (i.e., Dizziness Handicap Inventory and The Activities-specific Balance Confidence Scale) were poor indicators of peripheral vestibular status. In experiment two, auditory symptoms and auditory evoked potentials were examined to evaluate the prevalence of cochlear hydrops post blast exposure. The hypothesis for experiment two was that the blast-injured population would have a higher prevalence of cochlear hydrops than the general population. Results were consistent with a larger prevalence of cochlear hydrops post-blast exposure (8.1%) when compared to the general population (0.5 to 4%) and supported the initial hypothesis. Possible cochlear hydrops were identified in 16.2% of the blast injured population. Combining those individuals who were positive for cochlear hydrops and those who were possible for cochlear hydrops group, suggests that 24.3% of blast injured military personnel may be at risk for developing cochlear hydrops. Prolonged latency for wave III of the auditory brain stem response was observed in 41.2% of the blast injured population. Wave III abnormalities are suggestive for brain stem deficits. Overall, findings from the present investigation suggest that the inner ear is susceptible to damage/dysfunction post blast exposure but not to the extent initially hypothesized in the vestibular system. Data do support the cochlear hydrops hypothesis. The vast majority of abnormalities observed were consistent with central deficits and may highlight the brain stem as one region susceptible to blast injury.