Variations in cortical thickness with dementia severity in Alzheimer's disease.

Previous magnetic resonance imaging (MRI) studies have used volumetric methods to investigate cerebral atrophy and showed its linear pattern with the measure of dementia severity in Alzheimer's disease (AD). This study analyzed the phase- and region-specific changes in cortical thickness with dementia severity. In 43 normal controls and 60 AD patients with clinical dementia rating (CDR) (0.5, n=21; 1, n=28; 2, n=11), the cortical thickness was measured using automated surface-based analysis of MRI data. Statistical analyses were performed to investigate overall the hemispheric mean thicknesses as well as the topography of cortical atrophy based on vertices in the groups. No significant difference in cortical thickness was observed for the mild (from CDR=0.5 to 1) stage of dementia. In contrast, a significant reduction of cortical thickness occurred from CDR=1 to 2. Topographic analysis of cortical atrophy showed that the significant cortical thinning in CDR=0.5 relative to normal was found in most association cortices, with this being more extensive than previously reported. There were significant cortical atrophies between CDR=1 and 2 in the frontal, inferolateral temporal, inferior parietal lobule, medial occipital, and posterior-cingulated regions. Our results confirm and extend previous findings, suggesting that widespread cortical thinning occurs before the onset of dementia (from normal to CDR=0.5), and that once dementia starts, cortical atrophy in association cortices accelerates in moderate AD (from CDR=1 to 2).