11C-PIB PET imaging in Alzheimer disease and frontotemporal lobar degeneration

Background: The PET tracer C-11-labeled Pittsburgh Compound-B (C-11-PIB) specifically binds fibrillar amyloid-beta (A beta) plaques and can be detected in Alzheimer disease (AD). We hypothesized that PET imaging with C-11-PIB would discriminate AD from frontotemporal lobar degeneration (FTLD), a non-A beta dementia. Methods: Patients meeting research criteria for AD (n = 7) or FTLD (n = 12) and cognitively normal controls (n = 8) underwent PET imaging with C-11-PIB (patients and controls) and F-18-fluorodeoxyglucose (F-18-FDG) (patients only). C-11-PIB whole brain and region of interest (ROI) distribution volume ratios (DVR) were calculated using Logan graphical analysis with cerebellum as a reference region. DVR images were visually rated by a blinded investigator as positive or negative for cortical C-11-PIB, and summed F-18-FDG images were rated as consistent with AD or FTLD. Results: All patients with AD (7/7) had positive C-11-PIB scans by visual inspection, while 8/12 patients with FTLD and 7/8 controls had negative scans. Of the four PIB-positive patients with FTLD, two had F-18-FDG scans that suggested AD, and two had F-18-FDG scans suggestive of FTLD. Mean DVRs were higher in AD than in FTLD in whole brain, lateral frontal, precuneus, and lateral temporal cortex (p < 0.05), while DVRs in FTLD did not significantly differ from controls. Conclusions: PET imaging with C-11-labeled Pittsburgh Compound-B (C-11-PIB) helps discriminate Alzheimer disease (AD) from frontotemporal lobar degeneration (FTLD). Pathologic correlation is needed to determine whether patients with PIB-positive FTLD represent false positives, comorbid FTLD/AD pathology, or AD pathology mimicking an FTLD clinical syndrome.