Using Post-Traumatic Amnesia To Predict Outcome after Traumatic Brain Injury.

Duration of post-traumatic amnesia (PTA) has emerged as a strong measure of injury severity after traumatic brain injury (TBI). Despite the growing international adoption of this measure, there remains a lack of consistency in the way in which PTA duration is used to classify severity of injury. This study aimed to establish the classification of PTA that would best predict functional or productivity outcomes. We conducted a cohort study of 1041 persons recruited from inpatient admissions to a TBI rehabilitation center between 1985 and 2013. Participants had a primary diagnosis of TBI, emerged from PTA before discharge from inpatient hospital, and engaged in productive activities before injury. Eight models that classify duration of PTA were evaluated-six that were based on the literature and two that were statistically driven. Models were assessed using area under the receiver operating characteristic curve (AUC) as well as model-based Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) statistics. All categorization models showed longer PTA to be associated with a greater likelihood of being nonproductive at 1 year after TBI. Classification systems with a greater number of categories performed better than two-category systems. The dimensional (continuous) form of PTA resulted in the greatest AUC, and lowest AIC as well as BIC, of the classification systems examined. This finding indicates that the greatest accuracy in prognosis is likely to be achieved using PTA as a continuous variable. This enables the probability of productive outcomes to be estimated with far greater precision than that possible using a classification system. Categorizing PTA to classify severity of injury may be reducing the precision with which clinicians can plan the treatment of patients after TBI.