In vivo fibrillar β-amyloid detected using [¹¹C]PiB positron emission tomography and neuropathologic assessment in older adults

Background: In demented older adults, in vivo amyloid imaging shows agreement with diagnostic neuropathologic assessment of β-amyloid (Aβ). However, the extent of agreement in nondemented older adults remains unclear. Objective: To compare Aβ quantified using in vivo carbon 11-labeled Pittsburgh Compound B positron emission tomography and postmortem neuropathologic assessment of Aβ in older adults. Design: Case series. Setting: Community-dwelling older adults who came to autopsy. Participants: Five nondemented and 1 demented participant from the Baltimore Longitudinal Study of Aging. Main Outcome Measure: Agreement between the mean cortical distribution volume ratio and the Consortium to Establish a Registry for AD (CERAD) neuritic plaque (NP) score used for pathologic diagnosis of Alzheimer disease. Results: Of the 6 participants, 4 had moderate NPs, 2 had sparse or no detectable NPs, and 3 had microscopic findings of cerebral amyloid angiopathy at autopsy. On in vivo imaging, the mean cortical distribution volume ratio ranged from 0.96 to 1.59. Although there was agreement between in vivo amyloid imaging and CERAD NP scores in participants with either high or negligible Aβ levels in vivo, only limited agreement was observed among those with intermediate levels of Aβ. The best overall agreement was achieved at a distribution volume ratio of 1.2. Conclusions: In older adults, variable agreement between in vivo imaging and CERAD NP score was observed. The limited agreement may, in part, reflect differences in typical measurements of Aβ using imaging compared with the CERAD neuropathologic protocol. Direct quantification of regional Aβ in relation to in vivo imaging is necessary to further enhance our understanding of the imaging-pathologic assessment correlation.