Cognitive Outcome 1 Year After Mild Traumatic Brain Injury: Results From the TRACK-TBI Study

Abstract

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 included 656 participants ≥17 years of age presenting to level 1 trauma centers within 24 hours of mTBI (Glasgow Coma Scale score 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 (below the ninth 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 participants with mTBI 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 vs 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, preinjury depression, and greater injury severity (all p < 0.05). The final multivariable prediction model included education, health insurance, preinjury depression, hyperglycemia, and Rotterdam CT score ≥3 and achieved an area under the curve 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 patients with mTBI vs 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.

Figure 1. TRACK-TBI Participant Flow Diagram

GCS = Glasgow Coma Scale; GOAT = Galveston Orientation and Amnesia Test; TBI = traumatic brain injury; TRACK-TBI = Transforming Research and Clinical Knowledge in Traumatic Brain Injury.

Figure 2. Cognitive Decline Status

Cognitive decline status among participants with mild traumatic brain injury (TBI) (A, without cognitive impairment; B, with cognitive impairment) and controls (C, without cognitive impairment; D, with cognitive impairment). Plots shows each individual patient's 1-year reliable change index (RCI) score that was used to define categorization of cognitive decline (i.e., the RCI from the test with the second greatest decline) after stratification by 1-year cognitive impairment status.

Figure 3. Prediction Models of Poor 1-Year Cognitive Recovery* Among Patients With mTBI

(A) Receiver operating characteristic curves for models 1 and 2. (B) Model 1 including baseline characteristics that differed between good and poor 1-year cognitive outcome at the p < 0.2 level (Tables 2 and 3). (C) Model 2 including baseline characteristics after backward stepwise regression using α = 0.05. *Defined as cognitive impairment (≥1 score on ≥2 of 3 tests meeting criteria for impairment), cognitive decline (≥1 score on ≥2 of 3 tests meeting criteria for decline), or both. For the prediction models, baseline characteristics were entered as binary variables with the following reference values as follows: White race, more than a high school (HS) education, working full-time/part-time/students, income $35,000, health insurance, no depression, no developmental disability, nonassault injury, Rotterdam score <3, emergency department (ED) glucose <200 mg/dL or not done, no diabetes, Glasgow Coma Scale (GCS) score ≥14, no anxiety, and negative toxicology screen. AUC = area under the curve; mTBI = mild traumatic brain injury.