Distant histories of mild traumatic brain injury exacerbate age-related differences in white matter properties

Abstract

We examined associations of distant histories of mild traumatic brain injury (mTBI) with non-linear and linear trajectories of white matter (WM) properties across a wide age range (23-77). Diffusion tensor imaging (DTI) data obtained from 171 Veterans with histories of clinically diagnosed mTBIs and 115 controls were subjected to tractography, isolating 20 major WM tracts. Non-linear and linear effects of age on each tract's diffusion properties were examined in terms of their interactions with group (mTBI and control). The non-linear model revealed 7 tracts in which the mTBI group's DTI metrics rapidly deviated from control trajectories in middle and late adulthoods, despite the injuries having occurred in the late 20s, on average. In contrast, no interactions between prior injuries and age were detected when examining linear trajectories. Distant mTBIs may thus accelerate normal age-related trajectories of WM degeneration much later in life. As such, life-long histories of head trauma should be assessed in all patients in their mid-to-late adulthoods, whether neurologically healthy or presenting with seemingly unrelated neuropathology.

Keywords: Aging; Diffusion Tensor Imaging (DTI); Mild Traumatic Brain Injury (mTBI); Tractography; White Matter.

Figure 1.

Tracts in which mTBI histories were associated with accelerated age effects. White matter tracts in which significant interactions between group and age² were detected using the non-linear model are presented from a representative participant. The scatter plots show the mTBI group’s accelerated trajectories of age-related differences in WM properties for all diffusion metrics in which group x age² interactions were observed. MD: Mean Diffusivity; RD: Radial Diffusivity; AD: Axial Diffusivity; l-ATR: left anterior thalamic radiation (pink); AF: arcuate fasciculus (green); r-ATR: right anterior thalamic radiation (blue); r-CST: right corticospinal tract (red); r-UF: right uncinate fasciculus (yellow); l-ILF: left inferior longitudinal fasciculus (brown); l-CST: left corticospinal tract (turquoise).