Longitudinal Assessment of Selective Motor Dysfunction in Service Members With Combat-Related Mild TBI

Introduction: Evaluations of clinical outcomes in service members with mild traumatic brain injury (TBI) sustained in combat have largely focused on neurobehavioral and somatic symptoms, neurocognitive functioning, and psychological/psychiatric health. Questions remain regarding other domains, such as gross or fine motor abilities, that could be impacted and are mission-critical to functional warfighters.

Materials and methods: The objective of the current study was to evaluate longitudinal motor function in U.S. Military personnel with and without mild TBI sustained in combat to assess the possible long-term impact. Data from the EValuation Of Longitudinal outcomes in mild TBI active duty military and VEterans (EVOLVE) study were leveraged for analysis. The EVOLVE study has evaluated and followed service members from combat and following medical evacuation with and without blast-related mild TBI, as well as blunt impact mild TBI, and noninjured combat-deployed service members, tracking 1-, 5-, and 10-year outcomes. Longitudinal demographic, neuropsychological, and motor data were leveraged. Cross-sectional differences in outcomes at each year among the 4 injury groups were assessed using rank regression, adjusting for age, education, sex, branch of service (Army vs. other), subsequent head injury exposure, and separation from service. To understand the possible performance impact of time on all the measures, mixed-effects rank regression was employed, assessing time with adjustments for group, age, education, subsequent head injury exposure, and service separation status, followed by Benjamini-Hochberg correction for multiple comparisons.

Results: Evaluation for cognitive performance across 19 primary measures of interest at 1, 5, and 10 years did not identify any significant differences; however, gross motor function was found to be significantly different across groups at all time points (adjusted P < .001 at 1 year, P = .004 at 5 years, and P < .001 at 10 years) with both TBI groups consistently performing slower on the 25-Foot Walk and Grooved Pegboard than the nonblast control groups. While there were no cross-sectional differences across groups, many cognitive and motor measures were found to have significant changes over time, though not always in the direction of worse performance. Selective motor impairment in both TBI groups was identified compared to nonblast controls, but all groups were also found to exhibit a level of motor slowing when comparing performance at 1- to 10-year follow-ups.

Conclusions: Assessment of gross motor function reflected a consistent pattern of significantly slower performances for blast and nonblast TBI groups compared to controls, over all follow-up intervals. Fine motor function performance reflected a similar significant difference pattern at 1- and 5-year follow-up intervals, with a reduced difference from control groups at the 10-year follow-up. Maintenance of high-level motor functions, including overall motor speed, coordination, and reaction time, is a primary component for active warfighters, and any motor-related deficits could create an increased risk for the service member or unit. While the service members in this longitudinal study did not meet criteria for any specific clinical motor-related diagnoses or movement disorders, the finding of motor slowing may reflect a subclinical but significant change that could be a focus for intervention to return to preinjury levels.