A 5-year longitudinal evaluation in patients with mild cognitive impairment by 11C-PIB PET/CT: a visual analysis

The aim of this study was to evaluate the cerebral amyloid distribution in patients with mild cognitive impairment (MCI), assessed by carbon-11-Pittsburgh compound B (C-PIB) PET/CT, after 5 years of follow-up.

Ten amnestic MCI (A-MCI) and four nonamnestic (NA-MCI) patients were studied by C-PIB PET/CT and re-evaluated 5 years later by a new C-PIB PET/CT. PET/CT scans were acquired 60-90 min after the administration of 555 MBq C-PIB and analyzed visually, to obtain a score of the cerebral cortical C-PIB retention in the frontal, basal ganglia (BG), temporoparietal (TP), occipital, posterior cingulate, and cerebellum areas. Initial and 5-year follow-up C-PIB retentions were compared.

Initially, 9/10 A-MCI patients were C-PIB positive and one was C-PIB negative. All four NA-MCI patients were C-PIB negative. Of the C-PIB-positive A-MCI patients, seven progressed to Alzheimer's disease dementia (AD-D), one to mixed dementia and one remained as A-MCI. The C-PIB-negative A-MCI patient remained as A-MCI. Of the four C-PIB-negative NA-MCI, one progressed to semantic dementia. All changes in C-PIB retention were of low intensity. The A-MCI patients who progressed to AD-D (n=7) showed an increase in C-PIB retention in the frontal (5/7), BG (3/7), TP (3/7), occipital (1/7), and posterior cingulate (1/7) regions. The A-MCI patient who progressed to mix dementia showed an increase in C-PIB retention in the frontal region. The C-PIB-positive A-MCI patient who remained as A-MCI showed an increase in C-PIB retention in the frontal, BG, and TP areas. The amyloid deposition in the anterior part of the brain (frontal, TP, and BG) increased more than that in the posterior part (occipital and precuneus) (7/9 vs. 2/9; P<0.05).

PIB retention increased predominantly in the frontal, BG, and TP areas. C-PIB-positive A-MCI patients mostly progressed to AD-D, showing similar topographic changes in their cerebral C-PIB pattern than the patient who remained as A-MCI.