PET amyloid ligand [11C]PIB uptake is increased in mild cognitive impairment

Background: Patients with mild cognitive impairment (MCI) have increased risk to develop Alzheimer disease (AD). In AD increased brain amyloid burden has been demonstrated in vivo with PET using N-methyl-[C-11]2-(4'-methylaminophenyl)-6-hydroxybenzothiazole ([C-11]PIB) as a tracer. Objective: To investigate whether patients with amnestic MCI would show increased [C-11]PIB uptake, indicating early AD process. Methods: We studied 13 patients with amnestic MCI and 14 control subjects with PET using [C-11]PIB as tracer. Parametric images were computed by calculating the region-to-cerebellum ratio in each voxel over 60 to 90 minutes. Group differences in [C-11]PIB uptake were analyzed with statistical parametric mapping (SPM) and automated region-of-interest (ROI) analysis. Results: The SPM analysis showed that patients with MCI had significantly higher [C-11]PIB uptake vs control subjects in the frontal, parietal, and lateral temporal cortices as well as in the posterior cingulate showing the most prominent differences. These results were supported by the automated ROI analysis in which MCI patients showed in comparison with healthy control subjects increased [C-11]PIB uptake in the frontal cortex (39% increase from the control mean, p < 0.01), the posterior cingulate (39%, p < 0.01), the parietal (31%, p < 0.01) and lateral temporal (28%, p < 0.001) cortices, putamen (17%, p < 0.05), and caudate (25%, p < 0.05). Individually, in the frontal cortex and posterior cingulate, 8 of 13 patients with MCI had [C-11]PIB uptake values above 2 SD from the control mean. MCI subjects having at least one APOE epsilon 4 allele tended to have higher [C-11]PIB uptake than MCI subjects without APOE epsilon 4. Conclusions: At group level the elevated N-methyl-[C-11]2-(4'-methylaminophenyl)- 6-hydroxybenzothiazole ([C-11]PIB) uptake in patients with mild cognitive impairment (MCI) resembled that seen in Alzheimer disease (AD). At the individual level, about half of the MCI patients had [C-11]PIB uptake in the AD range, suggestive of early AD process.