Microstructural White Matter Abnormalities Independent of White Matter Lesion Burden in Amnestic Mild Cognitive Impairment and Early Alzheimer Disease Among Han Chinese Elderly

Abstract

This study was designed to evaluate the microstructural integrity of white matter (WM) in amnestic mild cognitive impairment (MCI) and Alzheimer's disease (AD) among Han Chinese elderly using diffusion tensor imaging (DTI) technique, and to investigate the relationship between WM abnormalities and cognitive dysfunction. Sixty-four subjects (23 mild probable AD, 20 amnestic MCI, and 21 age-matched normal controls) who did not have visible WM lesion burden were analyzed. Fractional anisotropy (FA) and mean diffusivity were measured in normal-appearing WM (NAWM) using DTI with 64 encoding directions. The results were correlated with the scores of Mini-Mental State Examination (MMSE) and Cognitive Ability Screening Instrument (CASI). Statistical analysis showed the FA value in parietal WM was significantly lower in MCI compared to NC (P<0.001), and further decreased in AD compared to MCI (P=0.005). The lower FA and elevated mean diffusivity values were found in temporal WM, frontal WM, parahippocampal and posterior cingulate fibers of AD group compared to MCI and NC (all P<0.01). Canonical correlation analysis showed that the parietal FA values measured from all subjects were significantly correlated with the scores of CASI and MMSE (P<0.01). The results indicated that DTI can detect microstructural WM abnormalities in AD and amnestic MCI, and the measures were correlated with cognitive performance. In MCI, the abnormality was found to be limited within the parietal WM; and in AD a more widespread alteration was found in other brain regions as well.