Axonal Injury Predicts Neurodegeneration After Traumatic Brain Injury

Post by Cody Walters 

What’s the science?

Data from non-human animal models of traumatic head trauma suggest that axonal damage can induce neuronal cell death. However, there is no direct evidence that axonal injury triggers progressive neurodegeneration in humans. This week in Brain, Graham and colleagues, examined the relationship between diffuse axonal injury and neuronal cell death in human subjects. 

How did they do it?

The authors imaged the brains of 55 patients (and 19 healthy control participants) with moderate-severe traumatic brain injury (TBI). Anatomical magnetic resonance imaging (MRI) was used to assess white/gray matter volume (via the Jacobian determinant [JD]) while diffusion tensor imaging (DTI; a type of MRI scan) was used to measure axonal integrity (via fractional anisotropy [FA]). Baseline brain volume and axonal integrity were established ~3.5 years after TBI, and participants received a follow-up scan ~1 year later.

What did they find?

The authors found that TBI participants had greater axonal injury at both baseline and follow-up scans relative to controls. This reduction in white matter integrity was most prominent in the corpus callosum, superior and inferior longitudinal fasciculus, external capsule, and posterior limb of the internal capsule. Similarly, the authors found that TBI subjects had lower gray and white matter volume across most brain regions at both baseline and follow-up scans relative to controls. Interestingly, the authors showed that the degree of axonal injury predicted the degree of brain atrophy a year later (with a positive correlation between FA scores and JD scores). Finally, the authors sought to determine the relationship between brain atrophy and cognitive impairment by administering a memory test. They found that performance on the memory test correlated with the degree of brain atrophy (with higher memory scores corresponding to less brain atrophy).

What’s the impact?

This study provides direct evidence that axonal injury following moderate-severe TBI predicts brain atrophy in human subjects. These data are clinically significant because they reveal a novel approach that has the potential to improve the assessment of neurodegenerative risk following TBI.

Graham et al. Diffuse axonal injury predicts neurodegeneration after moderate–severe traumatic brain injury. (2020). Access the original scientific publication here.