Brain imaging with glucose ( 18 F-FDG) PET or blood flow (hexamethylpropyleneamine oxime) SPECT is widely used for the differential diagnosis of dementia, though direct comparisons to clearly establish superiority of one method have not been undertaken. Methods: Subjects with Alzheimer disease (AD; n 5 38) and dementia with Lewy bodies (DLB; n 5 30) and controls (n 5 30) underwent 18 F-FDG PET and SPECT in balanced order. The main outcome measure was area under the curve (AUC) of receiver-operating-characteristic analysis of visual scan rating. Results: Consensus diagnosis with 18 F-FDG PET was superior to SPECT for both dementia vs. no-dementia (AUC 5 0.93 vs. 0.72, P 5 0.001) and AD vs. DLB (AUC 5 0.80 vs. 0.58, P 5 0.005) comparisons. The sensitivity and specificity for dementia/no-dementia was 85% and 90%, respectively, for 18 F-FDG PET and 71% and 70%, respectively, for SPECT. Conclusion: 18 F-FDG PET was significantly superior to blood flow SPECT. We recommend 18 F-FDG PET be performed instead of perfusion SPECT for the differential diagnosis of degenerative dementia if functional imaging is indicated.

Overall, although studies suggest superiority of PET over SPECT, the evidence base for this is actually quite limited. We suggest that further direct comparative studies, including health economic and patient preference evaluations, are needed to help direct future service provision.

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