The Relationship Between Blast-related Hearing Threshold Shift and Insomnia in U.S. Military Personnel

Hearing loss and insomnia emerged as preeminent sources of morbidity among military service members and veterans who served in the recent Iraq and Afghanistan conflicts. Significant threshold shift (STS), an early indicator of hearing loss, has not been studied in relation to insomnia. This study’s objective was to examine the co-occurrence of STS and insomnia among U.S. military personnel with blast-related injury. Materials and Methods A total of 652 service members who were blast-injured during military operations in Iraq or Afghanistan between 2004 and 2012 were identified from the Blast-Related Auditory Injury Database. Pre- and post-injury audiometric data were used to ascertain new-onset STS, defined as 30 dB or greater increase for the sum of thresholds at 2,000, 3,000, and 4,000 Hz for either ear. Insomnia diagnosed within 2 years post-injury was abstracted from electronic medical records. Multivariable logistic regression analysis examined the relationship between STS and insomnia, while adjusting for age, year of injury, occupation, injury severity, tinnitus and concussion diagnosed in-theater, and PTSD. Results A majority of the study sample was aged 18-25 years (79.9%) and sustained mild-to-moderate injuries (92.2%). STS was present in 21.1% of service members. Cumulative incidence of diagnosed insomnia was 22.3% and 11.1% for those with and without STS, respectively. After adjusting for covariates, those with STS had nearly 2-times higher odds of insomnia (odds ratio (OR) = 1.91, 95% CI = 1.12-3.24) compared with those without STS. In multivariable modeling, the strongest association was between PTSD and insomnia (OR = 5.57, 95% CI = 3.35-9.26). A secondary finding of note was that military personnel with STS had a significantly higher frequency of PTSD compared with those without STS (28.1% vs. 15.2%). Conclusions Hearing threshold shift was associated with insomnia in military personnel with blast-related injury and could be used to identify service members at risk. Multidisciplinary care is needed to manage the co-occurrence of both conditions during the post-deployment rehabilitation phase. Future research should evaluate the specific mechanisms involved in this relationship and further explore the association between hearing threshold shift and PTSD.