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Characterizing ‘mild’ in traumatic brain injury with proton MR spectroscopy in the thalamus: Initial findings

Objective: Although most mild traumatic brain injury (mTBI) patients suffer any of several post-concussion symptoms suggestive of thalamic involvement, they rarely present with any MRI-visible pathology. The aim here, therefore, is to characterize their thalamic metabolite levels with proton MR spectroscopy (1H-MRS) compared with healthy controls. Methods: T1-weighted MRI and multi-voxel 1H-MRS were acquired at 3 Tesla from 20 mTBI (Glasgow Coma Scale score of 15–13) patients, 19–59 years old, 0–7 years post-injury; and from 17 age and gender matched healthy controls. Mixed model regression was used to compare patients and controls with respect to the mean absolute N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) levels within each thalamus. Results: The mTBI-induced thalamic metabolite concentration changes were under ±13.0% for NAA, ±13.5% for Cr and ±18.8% for Cho relative to their corresponding concentrations in the controls: NAA: 10.08 ± 0.30 (mean ± standard error), Cr: 5.62 ± 0.18 and Cho: 2.08 ± 0.09 mM. These limits represent the minimal detectable differences between the two cohorts. Conclusion: The change in metabolic levels in the thalamus of patients who sustained clinically defined mTBI could be an instrumental characteristic of ‘mildness’. 1H-MRS could, therefore, serve as an objective laboratory indicator for differentiating ‘mild’ from more severe categories of head-trauma, regardless of the presence or lack of current clinical symptoms.