GERIATRIC TRAUMATIC BRAIN INJURY AND ALZHEIMER'S DISEASE SHARE PATTERNS OF WHITE MATTER DECLINE

The patterns of white matter (WM) degradation following mild traumatic brain injury (mTBI) and Alzheimer's disease (AD) are insufficiently understood and the extent of their similarities and differences are unknown. In both conditions, diffusion tensor imaging (DTI) has measured decreased fractional anisotropy (FA) in the corpus callosum and cingulum bundle, compared to healthy control (HC) volunteers [1, 2]. Although mTBI may modulate AD risk factors, few studies have directly compared the white matter alterations associated with these two conditions. We utilized DTI and tract-based spatial statistics (TBSS) to examine WM FA differences between the following age- and sex-matched groups: (A) 33 chronic mTBI patients, (B) 67 AD patients and (C) 81 HC participants. T1-weighted magnetic resonance imaging (MRI) and DTI were acquired at 3 T. MRIs of mTBI volunteers were acquired both acutely and ∼6 months post-injury. Artefact correction (motion, eddy currents), FA calculation and TBSS were implemented using FSL software. Two one-sided t (TOST) tests of statistical equivalence were used to investigate whether FA distributions within the WM skeleton of the brain were statistically equivalent in chronic mTBI victims compared to AD patients. An effect size with Cohen's d < 0.3 was used to specify the equivalence bounds of the TOST tests. Within the WM skeleton of the brain, the FA means of both mTBI and AD groups each differed significantly from that of the HC group skeleton (p < 0.01, corrected). In the mTBI group, FA means were statistically equivalent to those of the AD group (p < 0.05, corrected) in the corpus callosum and inferior longitudinal fasciculus. These results suggest that, ∼6 months after injury, geriatric mTBI survivors and AD patients have statistically equivalent FA means along two major WM fasciculi in the brain. Future studies should attempt to fully characterize the relationship between mTBI, AD and their associated sequelae.