Role of β-Amyloidosis and Neurodegeneration in Subsequent Imaging Changes in Mild Cognitive Impairment

IMPORTANCE To understand how a model of Alzheimer disease pathophysiology based on beta-amyloidosis and neurodegeneration predicts the regional anatomic expansion of hypometabolism and atrophy in persons with mild cognitive impairment (MCI). OBJECTIVE To define the role of beta-amyloidosis and neurodegeneration in the subsequent progression of topographic cortical structural and metabolic changes in MCI. DESIGN, SETTING, AND PARTICIPANTS Longitudinal, observational study with serial brain imaging conducted from March 28, 2006, to January 6, 2015, using a population-based cohort. A total of 96 participants with MCI (all aged >70 years) with serial imaging biomarkers from the Mayo Clinic Study of Aging orMayo Alzheimer's Disease Research Center were included. Participants were characterized initially as having elevated or not elevated brain beta-amyloidosis (A+ or A-) based on C-11-Pittsburgh compound B positron emission tomography. They were further characterized initially by the presence or absence of neurodegeneration (N+ or N-), where the presence of neurodegeneration was defined by abnormally low hippocampal volume or hypometabolism in an Alzheimer disease-like pattern on (18)fluorodeoxyglucose (FDG)-positron emission tomography. MAIN OUTCOMES AND MEASURES Regional FDG standardized uptake value ratio (SUVR) and gray matter volumes in medial temporal, lateral temporal, lateral parietal, and medial parietal regions. RESULTS In the primary regions of interest (ROI), the A+N+ group (n = 45) had lower FDG SUVR at baseline compared with the A+ N-group (n = 17) (all 4 ROIs; P < .001). The A+ N+ group also had lower FDG SUVR at baseline (all 4 ROIs; P < .01) compared with the A-N-group (n = 12). The A+N+ group had lower medial temporal gray matter volume at baseline (P < .001) compared with either the A+ N-group or A-N-group. The A+ N+ group showed large longitudinal declines in FDG SUVR (P < .05 for medial temporal, lateral temporal, and medial parietal regions) and gray matter volumes (P < .05 for medial temporal and lateral temporal regions) compared with the A-N+ group (n = 22). The A+ N+ group also showed large longitudinal declines compared with the A-N- group on FDG SUVR (P < .05 for medial temporal and lateral parietal regions) and gray matter volumes (all 4 ROIs; P < .05) compared with the A+N-group. The A-N+group did not show declines in FDG SUVR or gray matter volume compared with the A+N-or A-N- groups. CONCLUSIONS AND RELEVANCE Persons with MCI who were A+N+ demonstrated volumetric and metabolic worsening in temporal and parietal association areas, consistent with the expectation that the MCI stage in the Alzheimer pathway heralds incipient isocortical involvement. The A-N+ group, those with suspected non-Alzheimer pathophysiology, lacked a distinctive longitudinal volumetric or metabolic profile.