Regional metabolic patterns in mild cognitive impairment and Alzheimer's disease: A 1H MRS study

Abstract

Background: Mild cognitive impairment (MCI) is a recently described transitional clinical state between normal aging and AD. Assuming that amnestic MCI patients had pathologic changes corresponding to an early phase and probable AD patients to a later phase of the disease progression, the authors could approximate the temporal course of proton MR spectroscopic (1H MRS) alterations in AD with a cross-sectional sampling scheme.

Methods: The authors compared 1H MRS findings in the superior temporal lobe, posterior cingulate gyri, and medial occipital lobe in 21 patients with MCI, 21 patients with probable AD, and 63 elderly controls. These areas are known to be involved at different neurofibrillary pathologic stages of AD.

Results: The N-acetylaspartate (NAA)/creatine (Cr) ratios were significantly lower in AD patients compared to both MCI and normal control subjects in the left superior temporal and the posterior cingulate volumes of interest (VOI) and there were no between-group differences in the medial occipital VOI. Myoinositol (MI)/Cr ratios measured from the posterior cingulate VOI were significantly higher in both MCI and AD patients than controls. The choline (Cho)/Cr ratios measured from the posterior cingulate VOI were higher in AD patients compared to both MCI and control subjects.

Conclusion: These findings suggest that the initial 1H MRS change in the pathologic progression of AD is an increase in MI/Cr. A decrease in NAA/Cr and an increase in Cho/Cr develop later in the disease course.

Figure 1

Location of the 8cm³ posterior cingulate, and medial occipital VOI's on a mid-sagittal T1 weighted localizing image (a), location of the 7.2 cm³ left superior temporal VOI on a coronal (b), and a saggital (c) T1 weighted localizing image.

Figure 2

Examples of proton spectra obtained from the posterior cingulate VOI with an echo time of 135 ms. in a control subject (top), an MCI (middle), and a probable AD patient (bottom). The NAA /Cr ratio is lower in the probable AD patient compared to both the MCI and the control subjects.

Figure 3

Scatter plot of NAA /Cr ratios obtained from the left superior temporal, posterior cingulate and medial occipital VOI's of control (C), MCI and probable AD subjects (TE=135 ms.). Horizontal bars show the group -mean values.

Figure 4

Examples of proton spectra obtained from the posterior cingulate VOI with an echo time of 30 ms. in a control subject (top), an MCI (middle), and a probable AD patient (bottom). The MI /Cr ratios are higher in the MCI patient compared to the control subject. The MI /Cr and Cho /Cr ratios are higher in the AD patient compared to both the MCI and the control subjects.

Figure 5

Scatter plot of MI /Cr ratios of control (C), MCI and probable AD subjects in the posterior cingulate VOI (TE=30 ms.). Horizontal bars show the group -mean values.