Amnestic mild cognitive impairment: structural MR imaging findings predictive of conversion to Alzheimer disease

Abstract

Background and purpose: Mild cognitive impairment (MCI) is considered by many to be a prodromal phase of Alzheimer disease (AD). We used voxel-based morphometry (VBM) to find out whether structural differences on MR imaging could offer insight into the development of clinical AD in patients with amnestic MCI at 3-year follow-up.

Materials and methods: Twenty-four amnestic patients with MCI were included. After 3 years, 46% had progressed to AD (n = 11; age, 72.7 +/- 4.8 years; women/men, 8/3). For 13 patients (age, 72.4 +/- 8.6 years; women/men, 10/3), the diagnosis remained MCI. Baseline MR imaging at 1.5T included a coronal heavily T1-weighted 3D gradient-echo sequence. Localized gray matter differences were assessed with VBM.

Results: The converters had less gray matter volume in medial (including the hippocampus) and lateral temporal lobe, parietal lobe, and lateral temporal lobe structures. After correction for age, sex, total gray matter volume, and neuropsychological evaluation, left-sided atrophy remained statistically significant. Specifically, converters had more left parietal atrophy (angular gyrus and inferior parietal lobule) and left lateral temporal lobe atrophy (superior and middle temporal gyrus) than stable patients with MCI.

Conclusion: By studying 2 MCI populations, converters versus nonconverters, we found atrophy beyond the medial temporal lobe to be characteristic of patients with MCI who will progress to dementia. Atrophy of structures such as the left lateral temporal lobe and left parietal cortex may independently predict conversion.

Fig 1.

VBM contrast between converters and nonconverters by using a simple t test (no covariates). Areas with more atrophy in converters are superimposed on the average gray matter template. No threshold is applied so that the full extent of the results can be appreciated. Converters have more atrophy of the medial and lateral temporal lobes bilaterally and of the frontal and parietal lobes. Thresholded results corrected for multiple comparisons by using random field theory are displayed in Tables 4 and 5.

Fig 2.

Rendering of the simple t test and full model (corrected for age, sex, NYU, and global gray matter) between MCI converters and nonconverters. The big yellow area on the left hemisphere denotes less gray matter (more atrophy) in the converters group, compared with nonconverters, as captured by the t test. After correcting for age, sex, global gray matter atrophy, and a neuropsychological measure that is a good predictor of conversion to AD (NYU), atrophy in the left lateral temporal lobe and left parietal regions remains statistically significant, depicted as red. Results were thresholded at P = .001 uncorrected for multiple comparisons for display purposes.

Fig 3.

Coronal multiplanar reconstructions of a structural T1-weighted MR imaging volume. There is slight hippocampal atrophy (open arrow) with concomitant widening of the collateral sulcus (closed kinked arrow), both signs of progressive MTA. Additionally note slight parietal atrophy (closed arrow), which adds independent predictive value for conversion from mild cognitive impairment to AD.