Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




Mild traumatic brain injury (MTBI) accounts for 80–90% of the nearly two million traumatic brain injuries (TBI) that occur each year. The psychological consequences of MTBI can be extensive and can persist well beyond the acute injury, profoundly impacting the lives of the individual, their families, and society. A substantial number of MTBI patients suffer depressive mood, fatigue, and poor sleep (i.e., behavioral symptoms) for weeks and months post-injury. These symptoms reduce quality of life and delay the return to previous cognitive and functional status. Behavioral symptoms of depressed mood, fatigue, and poor sleep commonly co-occur and thus may constitute a symptom cluster, defined as co-occurring symptoms which share a common influence on an outcome. Symptoms of depression, fatigue, and poor sleep may share a common inflammatory etiology, and may develop as a result of pro-inflammatory cytokine elevation that occurs post-injury and which may persist beyond the acute phase of injury. Inflammatory molecules from sites of injury or infection are known to signal the brain to engender inflammatory-related sickness behaviors, such as depressed mood, fatigue, and poor sleep. It is possible that these co-occurring symptoms synergize to negatively impact cognitive and functional recovery. Yet investigation of these behavioral symptoms as a cluster and their association with MTBI recovery is limited.

Purpose: The purpose of this project is to identify different behavioral profiles of MTBI patients based on the intensity of depressive mood, fatigue, and sleep quality, to determine

whether there are differences in cognitive and functional outcomes at six months post-MTBI among the identified behavioral cluster profiles, and to explore differences in the intensity of behavioral symptoms at six months post-MTBI based on SNP genotype.

Research Design: This was a secondary data analysis of the database from the International Traumatic Brain Injury Initiative—TRACK-TBI pilot, which previously recruited TBI patients from two level I trauma centers. That study enrolled a total of 600 TBI patients; 340 of which suffered MTBI and who will thus be considered for potential inclusion in the current study. Participants in the original TRACK-TBI pilot study completed a battery of psychometric and health-related instruments and provided a blood sample for genetic analysis; these data were available to accomplish the aims of the present study.

Sample and Setting: From the TRACK-TBI pilot database, we selected a convenience sample (n=340) of male and females (ages >18years) who suffered external force trauma to the head, and who had an MTBI with classification by emergency department arrival Glasgow Coma Scale (GCS) as follows: mild (GCS 13–15). Only individuals who had completed follow-up at three months and six months were eligible.

Statistical Analysis: Latent Class Analysis was used to identify subgroups of MTBI patients with behavioral symptom cluster, using items derived from the psychological battery completed by participants in the TRACK-TBI pilot study completed; the presence and intensity of behavioral symptom cluster was analyzed with respect to cognitive and functional recovery. An analysis of covariance was used to explore differences in the intensity of behavioral symptoms at six months post-MTBI based on SNP genotype. The outcomes of this study will build a foundation upon which to establish clinically based strategies to identify MTBI patients at risk for protracted recovery and to identify those who may require earlier and more intense intervention.

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Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.