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Published on: November 9, 2018
Unawareness of memory deficit in amnestic MCI: FDG-PET findings
Flavio Nobili1, Debora Mazzei, Barbara Dessi
1Clinical Neurophysiology Unit, Dept of Neurosciences, Ophthalmology and Genetics University of Genoa, Genoa, Italy. flaviomariano.nobili@hsanmartino.it
Abstract:
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 18F-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.
Insights
Individuals with amnestic mild cognitive impairment (aMCI) and unawareness of memory deficit show more severe brain hypometabolism, particularly in the posteromedial cortex. This pattern suggests a higher risk for developing Alzheimer's disease dementia.
Area of Science:
- Neuroscience
- Medical Imaging
- Cognitive Neurology
Background:
- Awareness of memory deficits is crucial for managing cognitive decline in amnestic mild cognitive impairment (aMCI).
- Understanding the brain's metabolic underpinnings of this awareness is vital for early diagnosis and intervention.
- Previous studies have explored brain changes in aMCI, but the specific metabolic correlates of awareness remain less understood.
Purpose of the Study:
- To investigate the brain's metabolic differences between patients with aMCI who are aware of their memory deficits and those who are unaware.
- To identify specific brain regions and metabolic patterns associated with the level of awareness of memory impairment in aMCI.
Main Methods:
- Utilized 18F-FDG-PET scans to measure brain metabolism in 42 aMCI outpatients and 29 healthy controls.
- Assessed awareness of memory deficit using the Memory Complaint Questionnaire (MAC-Q), categorizing patients into unaware (low MAC-Q) and aware (good MAC-Q) groups.
- Employed SPM2 for statistical analysis to compare brain metabolism between groups and correlate it with MAC-Q scores.
Main Results:
- A positive correlation between MAC-Q score and metabolism was observed in the posterior cingulate cortex, inferior parietal lobule, and other regions in the whole aMCI group.
- Patients with unawareness (aMCI/unaware) exhibited significant hypometabolism in widespread left and right hemisphere clusters, including precuneus and inferior parietal lobule, compared to controls.
- Patients with awareness (aMCI/aware) showed smaller hypometabolic clusters in the bilateral temporal lobe. Notably, aMCI/unaware patients had more pronounced hypometabolism in specific left hemisphere regions compared to aMCI/aware patients.
Conclusions:
- The posteromedial cortex is a critical network involved in the awareness of memory deficits in aMCI.
- Lower awareness of memory deficit in aMCI is associated with a more severe pattern of brain hypometabolism, resembling that seen in Alzheimer's disease.
- This severe hypometabolism in unaware aMCI patients may indicate an increased risk of progressing to dementia.
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