Alzheimer’s Disease on FDG PET

B. Posterior cingulate cortex and precuneus, followed by parietal and temporal cortex

In early Alzheimer's disease, FDG-PET hypometabolism first appears in the POSTERIOR CINGULATE CORTEX and PRECUNEUS — regions involved in default mode network function and early AD pathology. As AD progresses, hypometabolism spreads to the bilateral inferior parietal cortex and posterior temporal cortex. Primary motor and sensory cortices, basal ganglia, and cerebellum are relatively spared until late stages. This characteristic posterior-predominant pattern on FDG-PET (or perfusion SPECT) helps distinguish AD from frontotemporal dementia (frontal/anterior temporal) and Lewy body dementia (parieto-occipital, with posterior cingulate sparing — the 'cingulate island sign').