Brain metabolite concentration and dementia severity in Alzheimer's disease: A ¹H MRS study

Objective: ¹H-MRS studies have shown abnormalities in brain levels of myo-inositol (mI) and N-acetyl aspartate (NAA) in AD, but the relation of these abnormalities with dementia severity was not examined. The authors sought to determine whether altered brain levels of mI and other metabolites occur in mild AD and whether they change as dementia severity worsens. Methods: The authors used ¹H-MRS with external standards to measure absolute brain concentrations of mI, NAA, total creatine (Cr), and choline (Cho)-containing compounds in 21 subjects with AD and 17 age- and sex-matched controls in occipital and left and right parietal regions. Results: Concentrations of NAA were significantly decreased, whereas mI and Cr concentrations were significantly increased in all three brain regions in subjects with AD compared with controls. Higher concentrations of mI and Cr occurred even in mild AD. A discriminant analysis of the ¹H-MRS data combined with CSF volume measurements distinguished subjects with AD, ranging from mild to severe dementia, from controls with 100% correct classification. NAA concentration, though not other metabolites, was positively correlated with Mini-Mental State Examination score. Conclusion: The measurements with ¹H-MRS of absolute metabolite concentrations in the neocortex showed abnormal concentrations of brain metabolites in AD; these metabolite concentrations do not necessarily correlate with disease severity. Although changes in myo-inositol and creatine occur in the early stages of AD, abnormalities of N-acetyl aspartate do not occur in mild AD but progressively change with dementia severity. Further, subjects with mild AD can be differentiated from controls with ¹H-MRS.