Early proton magnetic resonance spectroscopy in normal-appearing brain correlates with outcome in patients following traumatic brain injury

The long-term clinical outcome following traumatic brain injury (TBI) can b e difficult to predict. Proton magnetic resonance spectroscopy (MRS) has pr eviously been used to demonstrate abnormalities in regions of white matter that appear normal on conventional imaging in patients following TBI. We re port MRI and MRS studies of 26 patients performed at an early time point fo llowing injury (mean 12 days, n = 21) and at a later time point (mean 6.2 m onths, n = 15). The proton MRS was acquired from the posterior part of a no rmal-appearing frontal lobe containing predominantly white matter using sti mulated echo acquisition mode to localize, with a relaxation time of 3000 m s and echo time of 30 ms. At both the early and late time points the N-acet ylaspartate/creatine ratio (NAA/Cr) was significantly reduced (P = 0.03, P = 0.005, respectively), the choline/creatine ratio (Cho/Cr) significantly i ncreased (P = 0.001, P = 0.004, respectively) and the myo-inositol/creatine ratio (Ins/Cr) significantly increased (P = 0.03, P = 0.03, respectively) compared with controls. There was a small, but significant, further reducti on (P = 0.02) in the NAA/Cr between the two studies in the 10 patients for whom data was available, at both time points. The NAA/Cr acquired at the ea rly time point significantly correlated with the clinical outcome of the pa tients, assessed using either the Glasgow outcome scale (P = 0.005, n = 17) or the disability rating scale (P < 0.001, n = 17). We conclude that there is a sustained alteration in NAA and Cho. These findings provide possible evidence for cellular injury (NAA loss reflecting neuroaxonal cell damage a nd raised Cho and Ins reflecting glial proliferation) not visible by conven tional imaging techniques. This may be relevant to understanding the extent of disability following TBI.