Alzheimer disease: Absolute quantification of cerebral metabolites in vivo using localized proton magnetic resonance spectroscopy

In vivo magnetic resonance spectroscopy of brain metabolites such as N-acetylaspartate and myo-inositol has been proposed for the diagnosis of Alzheimer disease. Thirty patients with probable Alzheimer disease as well as 22 elderly controls underwent quantitative proton magnetic resonance spectroscopy of parietal gray and white matter with use of a short-echo time localization technique (echo time, 20 ms; repetition times, 6000 and 3000 ms, 2.0 Tesla) providing access to the regional concentrations of N-acetylaspartate, creatine, choline-containing compounds, myo-inositol, glutamate, glutamine, and lactate. No statistically significant alterations of the metabolites were found in patients relative to controls. There were also no differences between patients with early and late onset of the disease and with respect to the presence of APOE-ε4 phenotype. A general trend for slightly decreased levels of N-acetylaspartate and creatine was not observed for their respective concentration ratios. In summary, the spectroscopic findings were in accord with known Alzheimer disease neuropathology, i.e., mild gliosis in white matter as well as mildly enhanced cortical atrophy in comparison to elderly controls. However, cortical atrophy with little or no N-acetylaspartate changes provided no evidence for a major decrease of neuronal density or loss of viable neurons. The data do not support the utility of proton magnetic resonance spectroscopy as an early diagnostic tool for Alzheimer disease.