The impact of FDG and amyloid PET-CT in a clinical setting consisting of patients with suspected dementia: the Ferrara experience

Purpose: To evaluate the impact of sequential use of PET-CT with 18F-FDG and 18F- Florbetapir (Eli LillyTM) in a clinical setting consisting of patients with cognitive impairment and suspected dementia referring to Ferrara University Hospital and to assess the accuracy of FDG and amyloid PET-CT to correctly lead clinicians during diagnostic work-up in this patient population. Subjects and methods: From our clinical cases of patients studied with PET for brain metabolism evaluation, we retrospectively extrapolated 42 subject (20M; 22F) who underwent both FDG and amyloid PET-CT from October 2015 to January 2017. The FDG-PET has always preceded the execution of PET with florbetapir. Before any scan the reference clinician filled out a form with the clinical suspicious and the diagnostic question. Data about clinical history, neuropsychological tests, neuro-imaging and patient treatment were all recorded for further evaluation. Studies were acquired on a Biograph mCT Flow PET-CT scanner (Siemens Healthcare) after 30 minutes post-injection of 18F-FDG (187±20MBq) and 45 minutes after administration of 18F-Florbetapir (338±47MBq). Images were interpreted by two trained nuclear physicians. Results: In our population mean MMSE before FDG PET-CT was 23.1 (11-30). Mean age of subjects at the time of FDG scan was 67 years (55-72) and mean follow-up was 342±272 days. FDG PET-CT was concordant with clinical suspicious in 19 patients (45.2%) and therapy was changed in 13 patients (31%) after FDG study. Furthermore, after the subsequent amyloid PET-CT, clinical orientation was compatible with Florbetapir results in 23/42 scans (54.8%) and therapy was modified in further 9 patients (21,4%). On the basis of clinical follow-up, final diagnosis was fully concordant with FDG PET-CT in 19/42 patients (45,2%) whereas was consistent with amyloid PET-CT results in 38/42 patients (90.5%). The accuracy of FDG PET-CT in diagnosis of Alzheimer disease (AD) was 71.4% (sensitivity 58.8% and specificity 71.4%); whereas amyloid accuracy was 90.5% (sensitivity 88.2%, specificity 92%). Moreover FDG accuracy for fronto-temporal dementia (FTD) was 88.1% (sensitivity 57.1%, specificity 94.3%); meanwhile amyloid scans in FTD patients show absence of deposition in 7/7 cases. Conclusion: In this study we found that both FDG and amyloid PET-CT are feasible and have a significant impact in “everyday” clinical practice. Together they have high accuracy in the diagnosis of AD and FTD and FDG PET-CT leads clinicians to change therapy in one third of patients whereas amyloid PET- CT, used as a next step after the FDG, shows very high correlation with the final diagnosis.