The objective of this study was to analyze differences in incidence and epidemiologic risk factors for significant threshold shift (STS) and tinnitus in deployed military personnel diagnosed with mild traumatic brain injury (mTBI) due to either a blast exposure or nonblast head injury. A retrospective longitudinal cohort study of electronic health records of 500 military personnel (456 met inclusion criteria) diagnosed with deployment-related mTBI was completed. Chi-square tests and STS incidence rates were calculated to assess differences between blast-exposed and nonblast groups; relative risks and adjusted odds ratios of developing STS or tinnitus were calculated for risk factors. Risk factors included such characteristics as mechanism of injury, age, race, military occupational specialty, concurrent diagnosis of posttraumatic stress disorder (PTSD), and nicotine use. Among blast-exposed and nonblast patients, 67% and 58%, respectively, developed STS, (P=.06); 59% and 40%, respectively, developed tinnitus (P<.001). Incidence of STS was 24% higher in the blast-exposed than nonblast group. Infantry service was associated with STS; Marine Corps service, PTSD, and zolpidem use were associated with tinnitus. Unprotected noise exposure was associated with both STS and tinnitus. This study highlights potential risk factors for STS and tinnitus among blast-exposed and nonblast mTBI patient groups.
Keywords: blast-exposed; deployment-related injury; hearing loss; mTBI; mild traumatic brain injury; nonblast head injury; significant threshold shift; tinnitus.