Magnetic resonance spectroscopy abnormalities in traumatic brain injury: A meta-analysis.BACKGROUND AND PURPOSE
 Despite traumatic brain injury (TBI) being common, evaluation with imaging remains challenging.  Magnetic resonance spectroscopy (MRS) shows promise in detecting changes of brain metabolite concentrations following TBI; however, currently there are only small studies available without conclusive evidence of the technique's efficacy.  The purpose of this systematic review and meta-analysis was to evaluate the association between TBI and MRS metabolite changes.


 A comprehensive literature search was performed looking for studies reporting brain metabolite concentrations in both TBI and control subjects.  Included studies reported values for both adult TBI and control subjects.  Cumulative and subgroup meta-analyses were performed using a random effects model.


 The literature search returned an initial 898 manuscripts, of which 36 (which included 748 unique subjects) met study criteria.  Cumulatively, NAA/Cr ratios in TBI patients showed a significant decrease as compared to controls (standardized mean deviation [SMD]=-0.88, P<0.0001).  When broken into subgroups by severity, the severe and mixed TBI subgroups showed decreases, but the mild TBI (mTBI) subgroup did not.  When stratified by time, a significant decrease was seen in the subacute and chronic phases but not the acute phase.  Cumulative post-TBI Cho/Cr levels were increased compared to controls (SMD=0.69, P=0.0002).  Significant changes were seen in all subgroups except the mild and mixed mTBI subgroups and the acute phase subgroup.


 CONCLUSION
 Current evidence shows that MRS is able to detect changes to metabolites following TBI, but not in patients with mTBI or in the acute stage.
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