Structural and functional brain changes in the default mode network in subtypes of amnestic mild cognitive impairment.

BACKGROUND: Various amnestic mild cognitive impairment (aMCI) subtypes have been identified as single domain (SD) or multiple domain (MD), with differential probabilities of progression to Alzheimer disease (AD). Detecting the differences in the alterations in gray matter (GM) and intrinsic brain activity between the subtypes of aMCI help to understand their pathophysiological mechanisms and was conducive to construct such potential biomarkers to monitor the progression of aMCI.

METHODS: In all, 22 normal controls (NCs), 18 patients with SD-aMCI, and 17 patients with MD-aMCI participated in the study. The amplitude of low-frequency fluctuations (ALFFs) during rest represented intrinsic brain activity. Voxel-based morphometry analysis was used to measure the GM volume.

RESULTS: The MD-aMCI showed reduced GM in hippocampus (Hip), parahippocampal gyrus (PHG), and other regions than SD-aMCI. The SD-aMCI had reduced GM only in Hip and PHG than in NC. The MD-aMCI showed decreased ALFF in posterior cingulate cortex (PCC) and precuneus and increased ALFF in anterior cingulate cortex (ACC), PHG, and Hip compared with both SD-aMCI and NC. However, no ALFF difference was found between SD-aMCI and NC. Neuropsychological measures were correlated with ALFF in PCC and ACC only in the MD-aMCI.

CONCLUSIONS: Patients with MD-aMCI displayed more severe GM atrophy and ALFF changes than patients with SD-aMCI. The results suggested that aMCI is heterogeneous and that MD-aMCI may be a prodromal stage which is more close to AD.