Medial temporal lobe atrophy on MRI scans and the diagnosis of Alzheimer disease

Abstract

Background: Despite convenience, accessibility, and strong correlation to severity of Alzheimer disease (AD) pathology, medial temporal lobe atrophy (MTA) has not been used as a criterion in the diagnosis of prodromal and probable AD.

Methods: Using a newly validated visual rating system, mean MTA scores of three bilateral medial temporal lobe structures were compared for subjects with no cognitive impairment (NCI) (n = 117), nonamnestic mild cognitive impairment (MCI) (n = 46), amnestic MCI (n = 45), and probable AD (n = 53). Correlations between MTA scores and neuropsychological test scores at baseline, and predictors of change in diagnosis at 1-year follow-up were evaluated.

Results: With NCI as the reference group, a mean MTA cut score of 1.33 yielded an optimal sensitivity/specificity of 85%/82% for probable AD subjects and 80%/82% for amnestic MCI subjects. MTA and Clinical Dementia Rating Sum of Boxes scores at baseline were independent and additive predictors of diagnosis at baseline, and of transition from NCI to MCI or from MCI to dementia at 1-year follow-up.

Conclusion: Medial temporal lobe atrophy (MTA) scores 1) distinguish probable Alzheimer disease (AD) and amnestic mild cognitive impairment (MCI) subjects from nonamnestic MCI and no cognitive impairment (NCI) subjects, 2) help predict diagnosis at baseline, and 3) predict transition from NCI to MCI and from MCI to probable AD. MTA scores should be used as a criterion in the clinical diagnosis of AD.

Figure 1 Visual rating system for assessing medial temporal atrophy (A) The three regions of interest are outlined in the right hemisphere in color (hippocampus = red; entorhinal cortex = blue; perirhinal cortex = green), all showing no atrophy (score = 0) in both hemispheres. (B) All structures have severe atrophy (score = 4), with the exception of the right perirhinal cortex, which has moderate atrophy.

Figure 2 Medial temporal atrophy from visual rating system vs clinical diagnosis Box plot of medial temporal atrophy score (average of left and right) for subjects diagnosed with no cognitive impairment (NCI), nonamnestic mild cognitive impairment (MCI), amnestic MCI, and probable Alzheimer disease (AD). The median visual rating system score is represented by a horizontal line within the shaded box. The top and bottom of the box represent the 75th and 25th percentiles. The lines that extend out the top and bottom are 1.5 times the interquartile range (IQR) (value of 75th minus 25th percentile) above and below the box. Open circles are outliers (1.5–3 times the IQR above the box). The asterisk is an extreme outlier (more than 3 times the IQR above the box).