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AMYLOID PET HAS GREATER CLINICAL IMPACT THAN FDG PET IN THE DIFFERENTIAL DIAGNOSIS OF AD AND FTD

      Background: Differentiating AD (Alzheimer's disease) and FTD (frontotemporal dementia) is a promising application of amyloid imaging. We prospectively assessed the clinical impact of florbetapir PET in this scenario, and compared to FDG PET, the current standard.
      Methods: Patients with suspected AD (N=24) or FTD (N=13) were assessed by behavioral neurology fellows and attending physicians at an academic dementia center (10 by fellows, 2 by attendings, 25 by both). Mean age was 63.6±7.6 and MMSE was 21.3±6.6. All patients underwent florbetapir PET and 35/37 underwent FDG PET. Scans were visually interpreted blinded to clinical information. Written reports of scan reads were released to clinicians sequentially using a balanced design (50% florbetapir results disclosed first, balanced between fellows and attendings). Clinicians independently rated their top clinical diagnosis, diagnostic confidence and management plan prior to PET and following disclosure of each scan result.
      Results: Florbetapir PET was positive in 63% of patients with suspected AD and negative in 85% of FTD patients. FDG visual reads agreed with the clinical diagnosis in 73% of AD and 69% of FTD patients. Florbetapir and FDG PET agreed in 86% of patients (κ=0.72). There was no relationship between the order in which scans were disclosed and concordance with pre-PET diagnosis (p>0.54). Fellows changed their primary clinical diagnosis in 15% of cases after florbetapir results were disclosed and 0% after FDG results disclosure (p<0.001). Attending physician diagnoses changed in 11% of patients following florbetapir results and 4% after FDG results (p=0.08). Clinicians reported high diagnostic confidence in 37% of patients pre-PET, 45% post-FDG PET and 71% post-florbetapir PET (p=0.004 vs. FDG). Changes in management were more frequent after florbetapir (32%) than FDG results disclosure (12%), but this was not significant (p=0.67). Changes in management included starting or stopping AD medications, referring patients to clinical trials or further clinical work-up. Clinicians reported that amyloid results were more helpful than FDG results in guiding clinical management in 76% of cases.
      Conclusions: Amyloid PET had greater clinical impact than FDG PET and should be considered the PET scan of choice for the discrimination of AD and FTD.