Cerebrocerebellar hypometabolism associated with repetitive blast exposure mild traumatic brain injury in 12 Iraq war Veterans with persistent post-concussive symptoms

Abstract

Disagreement exists regarding the extent to which persistent post-concussive symptoms (PCS) reported by Iraq combat Veterans with repeated episodes of mild traumatic brain injury (mTBI) from explosive blasts represent structural or functional brain damage or an epiphenomenon of comorbid depression or posttraumatic stress disorder (PTSD). Objective assessment of brain function in this population may clarify the issue. To this end, twelve Iraq war Veterans (32.0 ± 8.5 [mean ± standard deviation (SD)] years of age) reporting one or more blast exposures meeting American Congress of Rehabilitation Medicine criteria for mTBI and persistent PCS and 12 cognitively normal community volunteers (53.0 ± 4.6 years of age) without history of head trauma underwent brain fluorodeoxyglucose positron emission tomography (FDG-PET) and neuropsychological assessments and completed PCS and psychiatric symptom rating scales. Compared to controls, Veterans with mTBI (with or without PTSD) exhibited decreased cerebral metabolic rate of glucose in the cerebellum, vermis, pons, and medial temporal lobe. They also exhibited subtle impairments in verbal fluency, cognitive processing speed, attention, and working memory, similar to those reported in the literature for patients with cerebellar lesions. These FDG-PET imaging findings suggest that regional brain hypometabolism may constitute a neurobiological substrate for chronic PCS in Iraq combat Veterans with repetitive blast-trauma mTBI. Given the potential public health implications of these findings, further investigation of brain function in these Veterans appears warranted.

Figure 1

Magnetic resonance imaging brain templates (top row) and voxel-wise Z-score maps for each mTBI Veteran participant (S001-S012, lower rows) showing patterns of hypometabolism relative to community volunteer control group (n=12). Views are Right Lateral (RT LAT), Left Lateral (LT LAT), Right Medial (RT MED), Left Medial (LT MED), Superior (SUP), and Inferior (INF). Vertical bar shows image color vs. Z-score scale.

Figure 2

Magnetic Resonance Imaging brain template (top row) and Z-score map of cerebral glucose metabolism difference between mTBI Veteran group (n=12) and community volunteer control group (n=12) (bottom row). Views and vertical bar are the same as in Figure 1.