Neurochemical alterations of the entorhinal cortex in amnestic mild cognitive impairment (aMCI): a three-year follow-up study.

The neurochemical alterations in the entorhinal cortex have not yet been measured, even though the entorhinal cortex is the earliest involved brain region in aMCI. In this study, we investigated whether brain regions including the entorhinal cortex would show early involvement of neurochemical abnormalities in aMCI, and whether magnetic resonance spectroscopy (MRS) abnormalities might be a predictive marker of conversion of aMCI to Alzheimer's disease (AD). MRS was performed on 13 aMCI patients and 11 patients with no cognitive impairment (NCI). Localizing voxels were placed within the entorhinal cortex, hippocampus, posterior cingulate gyrus, and occipital white matter in the dominant hemisphere. N-acetyl aspartate/creatinine (NAA/Cr) ratios in the entorhinal cortex were significantly lower in aMCI patients than in NCI subjects. After a three-year follow-up, seven aMCI patients converted to AD and six remained stable. Baseline NAA/Cr ratios of entorhinal cortex were decreased in converters, compared to NCI. Our study suggested the entorhinal cortex is the earliest site that is subject to neurochemical alteration in aMCI patients, and baseline MRS metabolite ratios in the entorhinal cortex can be a marker for predicting conversion of aMCI to AD.