CHICAGO – Diffusion tensor imaging identified axonal damage in veterans more than 4 years after a blast-related traumatic brain injury in a phase I/II study.
None of the veterans had abnormalities on conventional CT or MRI, Thomas M. Malone reported at the annual meeting of the Radiological Society of North America.
Prior studies have shown that diffusion tensor imaging (DTI) identified white matter injuries in the middle cerebellar peduncles, cingulum bundles, and right orbitofrontal region of asymptomatic veterans with mild TBI less than 90 days post injury (N. Engl. J. Med. 2011;364:2091-100).
Images courtesy Mr. Thomas M. Malone and colleagues
MRI DTI scans of a healthy control participant
However, another study showed that the correlation between DTI findings and neuropsychological symptoms in the acute phase was inconsistent at 2.5 years (J. Neurotrauma 2010;27:683-94).
In the phase I portion of the current study, 10 veterans with blast-related mild TBI were evaluated at an average of 51.3 months after injury, along with 10 healthy controls.
MRI DTI scans of veteran with moderate TBI
Despite having normal findings on CT and MR imaging, veterans had significantly higher average DTI-derived fractional anisotropy (FA) values than did controls in the right posterior limb of the internal capsule (0.739 vs. 0.706; P less than .05) and left posterior limb of the internal capsule (0.777 vs. 0.716; P less than .05). FA values were similar between groups in the anterior limbs of the internal capsule and genu and splenium of the corpus callosum. These higher FA values differ from results found in DTI studies conducted during the acute phase of blast-related mild TBI, said Mr. Malone of St. Louis University.
Overall, veterans scored significantly lower than did controls on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), immediate memory index (81.6 vs. 99.8; P less than .01), visual-constructional index (82.9 vs. 100.2; P less than .05), and delayed memory index (81.5 vs. 97.4; P less than .05).
Significant correlations were found between internal capsule FA values and neuropsychological tests measuring attention, memory, and motor functioning, including the RBANS and grooved pegboard test, Mr. Malone said.
For the phase II portion of the study, the investigators increased the cohort to 21 mild TBI and 8 moderate TBI veterans and 19 healthy controls, and removed outliers with FA values more than 2 standard deviations above or below the mean.
Patrice Wendling/Frontline Medical News
Mr. Thomas M. Malone
In this analysis, average FA values were significantly lower in the splenium of the corpus callosum among veterans than in controls (0.777 vs. 0.79; P less than .05).
"Decreased FA values among the TBI group are perhaps indicative of fiber damage and may explain the chronic deficits observed in mild blast injuries," Mr. Malone said.
Recovery from long-term axonal injury is possible, but the brain has somewhat limited capabilities in repairing itself, said senior author Dr. Richard Bucholz, professor and vice chair of neurosurgery at St. Louis University.
"My general feeling is if it doesn’t repair at 51 months, it probably never repairs," he said in an interview.
Although DTI findings of long-term axonal injury have important implications in terms of rehabilitation and continued problems associated with TBI injuries, both men urged caution in interpreting the results.
"I wouldn’t want to sell this as a diagnostic test," Mr. Malone said in a press briefing. "These were between-group differences."
Future studies will require larger numbers of veterans and the use of more robust preprocessing software such as Tortoise from the National Institutes of Health, automated segmentation, and voxel-based morphometry analysis.
Mr. Malone and his coauthors reported having no relevant financial disclosures.