Background and Objectives: The objectives of this study were to develop and establish concurrent validity of a clinically relevant definition of poor cognitive outcome 1 year after mild traumatic brain injury (mTBI), to compare baseline characteristics across cognitive outcome groups, and to determine whether poor 1-year cognitive outcome can be predicted by routinely available baseline clinical variables.
Methods: Prospective cohort study of 656 participants aged 17+ years presenting to Level 1 trauma centers within 24 hours of mTBI (Glasgow Coma Scale [GCS] 13-15) and 156 demographically similar healthy controls enrolled in the Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study. Poor 1-year cognitive outcome was defined as cognitive impairment (<9th percentile of normative data on ≥2 cognitive tests, cognitive decline (change score [1-year score minus best 2-week or 6-month score] exceeding the 90% reliable change index on ≥2 cognitive tests), or both. Associations of poor 1-year cognitive outcome with 1-year neurobehavioral outcomes were performed to establish concurrent validity. Baseline characteristics were compared across cognitive outcome groups and backward elimination logistic regression was used to build a prediction model.
Results: Mean age of mTBI participants was 40.2 years, 36.6% were female, 76.6% were white. Poor 1-year cognitive outcome was associated with worse 1-year functional outcome, more neurobehavioral symptoms, greater psychological distress, and lower satisfaction with life (all-p<0.05), establishing concurrent validity. At 1-year, 13.5% of participants with mTBI had a poor cognitive outcome versus 4.5% of controls, p=0.003. In univariable analyses, poor 1-year cognitive outcome was associated with non-white race, lower education, lower income, lack of health insurance, hyperglycemia, pre-injury depression, and greater injury severity (all-p<0.05). The final multivariable prediction model included education, health insurance, pre-injury depression, hyperglycemia, and Rotterdam CT Score>3 and achieved an AUC of 0.69 (95% CI=0.62-0.75) for the prediction of a poor 1-year cognitive outcome, with each variable associated with >2-fold increased odds of poor 1-year cognitive outcome.
Discussion: Poor 1-year cognitive outcome is common, affecting 13.5% of mTBI patients versus 4.5% of controls. These results highlight the need for better understanding of mechanisms underlying poor cognitive outcome after mTBI to inform interventions to optimize cognitive recovery.