Methods: 34 patients with MCI, 21 with AD, and 24 healthy controls (HC) were included. All subjects underwent cognitive testing, ApoE genotype and 60-min dynamic [11C]-PIB PET. [11C]-PIB data was acquired from 35-60 min after injection. Distribution volume ratios (DVR) were calculated for 18 cortical regions using Logan graphical analysis. The patients were clinically followed up for 1-2 years after baseline and re-examined.

Results: Eleven (32%) of the 34 patients with MCI developed AD during the follow-up period (20.50±6.35 months). All of these converters had an increase in PIB retention at baseline, and mean DVR value in whole cortical regions was 2.31±0.29, similar to that of AD patients. The DVR value after baseline did not increase significantly in any cortical region. In contrast, 11 PIB positive patients with MCI remained relatively stable during this period although the mean cortical DVR did not significantly differ from MCI converters (2.09±0.32, n=11). None of the 6 MCI patients with an intermediate level of PIB retention and 6 MCI patients without increased PIB retention converted to AD. ApoEε4 was present in 13 (38%) of 34 patients with MCI. Ten (45%) of 22 PIB positive patients with MCI were ApoEε4 carriers, who did not have higher PIB retention. Seven (64%) of 11 converting MCI patients carried the ApoEε4 (p<0.05, chi-square), compared with 6 (26%) of 23 MCI non-converters.

Conclusions: The PIB-positive patients with MCI, who are ApoEε4 carriers, are more likely to faster develop AD. The cortical amyloid deposition associated with ApoE-ε4 allele may be a predicting biomarker of faster progression to AD.