Comparison of Brain Glucose Metabolism and Monoamine Oxidase B (MAO B) in Traumatic Brain Injury

OBJECTIVE: Positron emission tomography (PET) studies in patients with temporal lobe epilepsy have reported that hypometabolism in temporal regions is associated with elevated monoamine oxidase B (MAO B) probably reflecting gliosis. The purpose of this study was to examine a group of head trauma patients suffering from seizures and memory loss to determine whether hypometabolic regions show correspondingly elevated MAO B.METHODS: Seven patients with traumatic brain injury received PET scans with (18)FDG and [(11)C]L-deprenyl-D2 to measure regional glucose metabolism (LCMRglu) and MAO B respectively. Results were compared to a group of nine age-matched healthy controls. Hypometabolic regions were identified and MAO B values corresponding to these brain regions were determined. Averaged brain images for temporal regions for LCMRglu and MAO were also compared.RESULTS: LCMRglu values for temporal regions were reduced in patients relative to normal subjects. Of the 13 hypometabolic brain regions, 6 (46%) showed a corresponding elevation in MAO B. There was a trend for a significant inverse relationship between normalized LCMRglu and normalized MAO B values for medial temporal cortex. Glucose metabolism was significantly higher in lateral than medial temporal regions whereas the pattern was reversed for MAO B.CONCLUSION: MAO B images provide a markedly better delineation of the medial temporal regions than LCMRglu. There was not a consistent inverse relationship between metabolism and MAO B as had been reported in PET studies of epileptogenic temporal lobes with [(11)C]L-deprenyl-D2 and (18)FDG indicating that prospective studies are needed to determine the pathophysiology of hypometabolic lesions in head trauma.