Unawareness of memory deficit in amnestic MCI FDG PET findings

To unveil the brain metabolic correlates of (un)awareness of memory deficit in subjects with amnestic mild cognitive impairment (aMCI), forty-two outpatients underwent brain 18 F-FDG-PET. Awareness of memory deficit was assessed with the Memory Complaint Questionnaire (MAC-Q), identifying two groups: low (MCI/unaware; 17 patients) and good (MCI/aware; 25 patients) aMCI awareness. Twenty-nine age-matched healthy subjects represented the control group. SPM2 was used to assess the correlation between brain metabolism and MAC-Q score, for comparisons between each patient group and controls, and between aMCI/unaware and aMCI/aware groups. The two aMCI groups were comparable in terms of age, gender, education, depression, and neuropsychological tests scores. In the whole 42-patient group, a positive correlation was found between MAC-Q score and metabolism in posterior cingulate cortex in both hemispheres and in inferior parietal lobule, middle cingulate cortex, precuneus and angular gyrus in the left hemisphere. Compared to controls, hypometabolism was found in aMCI/unaware in three large clusters, including precuneus, inferior parietal lobule and superior occipital gyrus, in the left hemisphere, and in inferior parietal lobule, angular gyrus and middle temporal gyrus in the right hemisphere. Smaller clusters of hypometabolism were found in bilateral temporal lobe in aMCI/aware. Hypometabolism in inferior parietal lobule, angular gyrus and superior temporal gyrus in the left hemisphere was highlighted in aMCI/unaware versus aMCI/aware. The significant correlation in all 42 aMCI patients points to posteromedial cortex as a key node of the network being involved in awareness of memory deficit. Patients with low awareness show a more severe hypometabolic pattern, typical of Alzheimer's disease and therefore could be more at risk of developing dementia.