Background: We encountered eight early amnestic mild cognitive impairment (aMCI) patients (early MCI group) who did not fulfill the diagnostic criteria for aMCI. We compared the scores of neuropsychological examinations as well as the cerebral metabolic rate for glucose consumption (CMRglc) decrease on 18F-FDG PET examination between the early MCI group and 10 aMCI patients (MCI group) or six normal elderly subjects (normal group), to examine whether the current diagnostic criteria can detect early-stage aMCI.
Methods: The three groups underwent Mini-Mental State Examination (MMSE), Wechsler Adult Intelligence Scale – Third Edition (WAIS-III), Wechsler Memory Scale Revised (WMS-R), magnetic resonance imaging and 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) examinations.
Results: The early MCI group did not show significant memory impairment of 1.0 SD or other cognitive dysfunctions on neuropsychological examinations, and did not fulfill the diagnostic criteria of aMCI. With one-way anova and Tukey's HSD post-hoc test, the early MCI group showed the highest scores for WAIS-III, whereas the MCI group showed the lowest scores for WMS-R, although there were no significant differences between the early MCI and normal groups. In order to show a discrepancy in scores between WAIS-III and WMS-R, we subtracted the scores of WMS-R from WAIS-III. Consequently, the normal group showed significantly smaller differences in scores than the other groups, although there were no significant differences between the early MCI and MCI groups. 18F-FDG PET recognized a CMRglc decrease in the posterior cingulate gyrus and/or part of the parietotemporal area in both the MCI and early MCI groups, of which the extent and magnitude were weaker in the early MCI group. The normal group did not show a significant CMRglc.
Conclusions: The early MCI group should be included in aMCI not only based on the discrepancy between intelligence and memory scores, but also based on the 18F-FDG PET findings. The combination of these examinations would make it possible to diagnose early-stage aMCI.