DTI Shows Brain Changes in Mild Head Injury

July 28, 2014

A new study using diffusion tensor imaging (DTI) has demonstrated changes in the white matter of patients within days of sustaining a mild head injury and has shown that these changes correlate with reduced performance on cognitive tests.

In a longitudinal study of patients studied using DTI at 6 days after injury and 1 year later, they found that acute mild to moderate traumatic brain injury was characterized by increased tissue fractional anisotropy, a measure of the direction of water movement through the tissue, "which represents a clear neurobiological link between cognitive dysfunction and white matter injury after mild/moderate injury," the researchers conclude.

"Our research identifies a biological process that could explain the cognitive problems seen after mild head injury," said senior author, Andrew M. Blamire, PhD, Newcastle University, United Kingdom.

"We have shown that this technology is capable of demonstrating the extent of damage to the brain even after a mild head trauma," Dr. Blamire commented.

The study was published in Neurology on July 16.

Clearly Visible Changes

He explained that the technologies currently used to visualize head injuries —MRI or computerized tomography — do not give an accurate picture of damage to the brain. "This DTI scan reveals much greater extent of injury. We saw clearly visible changes and the magnitude of those changes related to the ability to perform cognitive tests."

Dr. Blamire explained that most patients with mild head injury will have some short-term cognitive dysfunction, and for some this will persist for months or years. "This is the first time that such damage has been visualized in the brain at such an early time point after a mild head injury. The majority of work in this area has previously focused on severe head injuries. Mild head injury has been very underinvestigated as we haven't had the ability to measure it."

The DTI technology is already used to measure ischemic damage in stroke patients and has also been shown useful in severe head injuries. "If we can reconfirm our findings then it could help stratify patients with mild head injuries in the clinic," he suggested. "In future it might be possible to select out patients from such a scan who are at higher risk of long-term cognitive problems, and then they could be offered appropriate support."

For the study, 53 patients were scanned an average of 6 days after head injury, and 23 of these patients were rescanned 1 year later. They were compared with 33 controls matched for age and education. At the time of scanning, all participants also underwent cognitive testing.

Results showed that the patients with mild and moderate head injury had extensive increases in mean diffusivity (water mobility) within the white matter, which were accompanied by increased fractional anisotropy (the direction of water movement), with decreased radial diffusivity. This was strongly correlated with poorer performance on the Verbal Letter Fluency cognitive test.

Different Mechanism to Severe Head Injury?

Dr. Blamire explained that the white matter is ordered and structured. "Diffusion technology measures how far water molecules move within the white matter. It has been shown that in patients with severe head injury there is a disordered movement of water. In contrast, in this study in patients with mild head injury there was a more ordered movement of water." He said the reasons for this were not well understood, but the researchers suspect it could be due to anti-inflammatory glial cells moving in to help with the injury.

Imaging results at 12 months supported the wider literature in chronic brain injury, with a more chaotic pattern of water movement driven by an underlying increase in radial diffusivity, which the researchers say is evidence that the axonal membrane and myelin sheath have disintegrated.

Cognitive testing showed that while some patients did return to normal and recovered cognition, some patients still had problems, although there wasn't a significant difference compared with control in the whole group.

"This longitudinal study has produced a comprehensive picture of the diffusion imaging changes after mild/moderate TBI and how these can relate to cognition in a large cohort of patients," the researchers conclude. "Detailed analysis of the complete set of diffusion metrics suggests that gliosis rather than cytotoxic edema is most consistent with changes in these metrics after acute, mild TBI."

"We have detected a change in white matter in patients with mild head injury, which correlates with reduced cognition," Dr. Blamire told Medscape Medical News. "The next step is to try and repeat these observations. We have got funding for another 30 patients. Then we would like to do an interventional study in which patents would be stratified by degree of injury shown and see if we can have an impact on outcome with cognitive training."

Funding for the study and a studentship to I.D.C. were provided by Sir Jules Thorn Charitable Trust Biomedical Research Award. The authors have disclosed no relevant financial relationships.

Neurology. Published online July 16, 2014. Abstract

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