The Role of Preinjury Cognitive Function in Future Traumatic Brain Injury and Functional Recovery

Cognitive function (CF) is likely an important determinant of outcome after traumatic brain injury (TBI) and a predisposing factor for TBI. Previous research measures CF using estimates of pre-TBI CF. We studied the association between measured preinjury CF and functional outcome after injury and whether CF differed based on future TBI.

This retrospective, observational study assessed the role of preinjury CF in post-TBI functional outcome and the association with future TBI in Finnish male conscripts. We included patients with TBI treated at Helsinki University Hospital between December 1997 and December 2020. We operationalized CF with the Finnish Defense Forces P1 test, which measures visuospatial, verbal, and arithmetic abilities (range 1-9, higher scores indicating higher CF). We assessed functional outcome as the 6-month Glasgow Outcome Scale (GOS, range 1-5, higher scores indicating better functional outcome). Only patients with TBI who had a pre-TBI CF and functional outcome assessment were included. We defined GOS 1-3 as unfavorable outcome and GOS 1-4 as incomplete recovery. We used logistic regression to assess the association between CF and functional outcome, adjusting for age at hospital admission for TBI and TBI severity. We used Mann-Whitney U tests to compare CF between patients with TBI and non-TBI controls to examine whether CF differed based on future TBI.

Of 547 male (0% female) patients with TBI who had CF assessed, 377 had pre-TBI CF and available GOS (69%); of these patients, 18% had unfavorable outcome and 55% incomplete recovery. The median age at time of injury was 40 years (interquartile range [IQR], 31-47), 49% had Glasgow Coma Scale 3-12, and a median P1 score of 5 (IQR, 4-6). We found that CF was associated with incomplete vs complete recovery (OR, 0.86; 95% CI, 0.76-0.96). Non-TBI controls had significantly higher CF than patients with TBI: both p < 0.001, r = 0.46 (95% CI, 0.38-0.55) and r = 0.44 (95% CI, 0.36-0.52).

CF was associated with incomplete recovery after TBI. Patients with TBI had lower CF than non-TBI controls, suggesting that CF may influence susceptibility to TBI. However, the generalizability of our findings may be limited because our study involves a single center and includes only male patients.