Comparison of clinical outcomes 1- and 5-years post-injury following combat concussion.

Objective To compare 1-year and 5-year clinical outcomes in 2 groups of combat-deployed-non-brain-injured service members to 2 groups of combat-related concussion to better understand long-term clinical outcome trajectories. Methods This prospective, observational, longitudinal multi-cohort study examined 4 combat-deployed groups: non-head-injured controls with or without blast exposure, and patients with combat concussion arising from blast or blunt trauma. 1-year and 5-year clinical evaluations included identical batteries for neurobehavioral, psychiatric, and cognitive outcomes. Three hundred forty-seven participants completed both time points of evaluation. Cross-sectional and longitudinal comparisons were assessed. Overall group-effect was modelled as a four-category variable with rank regression adjusting for demographic factors using a two-sided significance threshold of 0.05, with post-hoc Tukey p-values calculated for the pairwise comparisons. Results Significant group differences in both combat concussion groups were identified cross-sectionally at 5-year follow-up compared to controls in domains of neurobehavioral-NRS (Cohen9s-d, −1.10 to −1.40, CIs [−0.82: −1.32] to [−0.97: −1.83] by group), and psychiatric-CAPS (Cohen9s-d, −0.91 to −1.19, CIs [−0.63: −1.19] to [−0.76: −1.62] by group) symptoms with minimal differences in cognitive performance. Both combat concussion groups also showed clinically significant decline from 1-to-5-year evaluation (66%–76% neurobehavior-NRS; 41%–54% psychiatric-CAPS by group). Both control groups fared better but a subset also had clinically significant decline (37%–50% neurobehavior-NRS; 9%–25% psychiatric-CAPS by group). Conclusions There was an evolution not resolution of symptoms from 1-to-5-year evaluation challenging the assumption that chronic stages of concussive injury are relatively stable. Even some of the combat-deployed controls worsened. The evidence supports new considerations for chronic trajectories of concussion outcome in combat-deployed service members.