Metabolic and microstructural brain alterations associated with occupational blast exposure

Repeated occupational exposure to low-level blast may pose a risk to the neurological health of service members. To date, no studies have specifically investigated the effects of such repetitive exposure using fluorodeoxyglucose positron emission tomography (FDG-PET). This study aims to characterize cerebral metabolic alterations associated with occupational blast exposure, accounting for confounding factors such as posttraumatic stress disorder (PTSD) symptoms and aging. Male service members with chronic mild TBI (mTBI) were categorized into high-risk (HR; n = 204) and low-risk (LR; n = 68) blast exposure groups based on their military occupational specialty. FDG-PET and diffusion tensor imaging (DTI) data were analyzed using region-of-interest (ROI) and voxelwise methods. Statistical models included age and PTSD symptom severity as covariates. Compared to the LR group, ROI analyses revealed higher FDG uptake in the left pallidum, caudate, and ventrolateral prefrontal cortex in the HR group. These elevations in metabolic activity may reflect compensatory mechanisms in response to neurophysiological disruption following blast exposure. Voxelwise analysis showed lower FDG uptake in the HR group within white matter, predominantly in the right hemisphere, including the corpus callosum, anterior thalamic radiation, inferior and superior longitudinal fasciculi. Corresponding DTI findings showed higher fractional anisotropy (p = 0.0025) and axial diffusivity (p = 0.024) in these regions. Furthermore, leftward metabolic lateralization was observed in the pallidum, with the HR group (Cohen's d = 1.36, 95% CI [1.14, 1.57]) exhibiting greater metabolic asymmetry than the LR group (Cohen's d = 1.16, 95% CI [0.79, 1.51]). Findings from this study reveal metabolic and microstructural alterations associated with occupational blast exposure in service members with mTBI.