Grey-matter atrophy in Alzheimer's disease is asymmetric but not lateralized

In Alzheimer's disease (AD), brain atrophy has been proposed to be left lateralized. Here, we reinvestigated the asymmetry and lateralization (i.e., asymmetry directed toward one hemisphere) of grey-matter (GM) distribution in 35 patients with AD, 24 patients with amnestic mild cognitive impairment (aMCI, a state of increased risk for AD), and 30 age-matched healthy controls (HC). We analyzed GM distribution by applying voxel-based morphometry (VBM) including analyses for asymmetry and lateralization. When comparing MCI with AD patients, VBM revealed GM loss in the entorhinal, temporoparietal, dorsofrontal, and occipital cortices as well as in the precuneus; when comparing HCs with MCI patients, we found similar differences, which were less pronounced especially within the temporoparietal cortex and precuneus. Analyses of regional asymmetry and regional lateralization as well as global lateralization did not yield significant results. However, lobar asymmetry of the temporal, parietal, and occipital lobes increased from HC to AD. Moreover, in aMCI and AD patients, performance of language-based neuropsychological tests correlated with lateralization of GM loss to the left hemisphere. We conclude that, in principle, brain atrophy in AD is asymmetric rather than lateralized. At the individual level however, asymmetry contributes to cognitive deficits.