Mild traumatic brain injury outcomes vary significantly

Long-term outcomes for combat veterans and active-duty service members who sustained mild traumatic brain injury vary widely, a 10-year follow-up study has found. 

“We found that service members who had mild traumatic brain injury fell into different TBI subtypes, with many showing resiliency but important subgroups at risk for later decline,” said the lead researcher on the study, Christine Mac Donald, a professor of neurosurgery at the University of Washington School of Medicine in Seattle. 

The findings were published Dec. 10 in JAMA Network Open. They might help identify patients at high risk of developing psychological, neurobehavioral or cognitive problems before they manifest, Mac Donald said. 

“We identified evolving clinical outcomes in service members which could allow for stratification into focused intervention strategies years before they start to notably decline, essentially flipping treatment concepts on their head and being proactive instead reactive,” she said.  

The study followed 288 service members from the time of their deployment in Iraq and Afghanistan until 10 years later, with evaluations at one, five and 10 years.  Mild traumatic brain injury diagnosis aligned with the Department of Defense definition: exposure to blast or blunt trauma resulting in loss of consciousness of less than 30 minutes, alteration of consciousness of less than 24 hours, post-traumatic amnesia of less than 24 hours and a normal CT scan at the time of injury. 

At each visit, the patient evaluation included an MRI scan and assessments of 34 psychological, cognitive and neurological/neurobehavioral functions to track the trajectory of their clinical course over time.  

Two groups with combat-related mild traumatic brain injuries were examined: 137 had a blast exposure and 21 had a blunt trauma. For comparison, the team also evaluated two control groups who did not have a history of traumatic brain injury: 36 with a blast exposure and 94 without.  

Using the clinical outcome data, the authors found that service members fell into four clusters or subtypes. One group was designated as resilient because they had no significant cognitive dysfunction or neurobehavioral or psychological symptoms after 10 years. Most people in the resiliency subtype were part of the control groups, but 36% were service members with mild TBI. This observation suggests that mild TBI does not necessarily result in a poor long-term outcome.   

This is an important finding, Mac Donald said, because there are concerns that mild TBIs increase the risk of neurodegeneration and dementia later in life. 

The other three subtypes included:  

• Those who did not have cognitive dysfunction but did have mild neurobehavioral and psychological symptoms.  
• Those who had moderate cognitive dysfunction with substantial neurobehavioral and psychological symptoms.  
• Those who had severe cognitive dysfunction and moderate neurobehavioral and psychological symptoms.  

Interestingly, Mac Donald said, these profile subtypes did not emerge with full clarity until the last of the three clinical evaluations. 

The MRI scans also detected differences in the volume of some brain structures, such as the cerebellum and brainstem, involved in learning and emotion. This was particularly the case among those who developed severe cognitive dysfunction. 

Unlike clinical outcomes, brain imaging differences by subtype were detected in the earliest MRI scans at enrollment. Whether they were the result of the mild TBI or reflected differences that had existed before injury is unclear, Mac Donald said. She added that brain scans obtained earlier in clinical care might help identify people at higher risk of developing poor outcomes. 

“These service men and women were injured fighting for our country,” Mac Donald said. “We owe it to them to better understand these differences in mild TBI outcomes to give them the best shot at sustained recovery and long-term quality of life.” 

The data were collected as part of the ongoing Evaluation of Longitudinal Outcomes in Mild TBI Active-Duty U.S. Military and Veterans (EVOLVE) study.  Funding for the study was provided by the National Institute of Neurological Disorders and Stroke (RO1NS091618).  

Written by Michael McCarthy.

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