18F‐Flortaucipir PET imaging compared with autopsy in a clinically and pathologically heterogeneous group of patients with neurodegenerative dementias

Background We aimed to investigate the utility of qualitative visual rating of 18F‐flortaucipir tau (FTP) PET to predict the neuropathologic diagnosis in patients with a diverse array of clinical syndromes who were followed to autopsy. Method FTP PET, PiB PET, and high resolution T1 MRI scans were rated independently by visual inspection by two raters blinded to clinical diagnosis in n=22 subjects, including patients with a clinical syndrome of amnesic dementia (n=1), posterior cortical atrophy (n=2), logopenic primary progressive aphasia (n=1), nonfluent PPA (n=4), semantic PPA (n=3), corticobasal syndrome (n=1), behavioral variant frontotemporal dementia with a MAPT mutation (n=3) or GRN mutation or C9orf72 expansion (n=2), progressive supranuclear palsy (n=4), or dementia with Lewy bodies (DLB; n=1). FTP scans were classified using a two‐tiered system. First‐tier classification distinguished scans as either “abnormal‐>high‐confidence AD,” “abnormal‐>mildly‐elevated uptake,” or “normal.” Among scans classified as “abnormal‐>high‐confidence AD,” second‐tier classification distinguished “typical AD,” “atypical AD,” or “late‐stage AD.” Among scans classified as “abnormal‐>mildly‐elevated uptake,” second‐tier classification distinguished “possible early‐stage AD,” “possible FTLD,” or “indeterminate.” Result All individuals with ADNC as the primary pathology were classified as abnormal‐>high confidence AD. All individuals with FTLD as the primary pathology were classified as abnormal‐>mildly‐elevated uptake‐>possible FTLD, but cases with FTLD‐TDP43 pathology were not distinguishable based on FTP from those with FTLD‐tau, supporting prior observations. Additional details will be reported on these and the other cases. Conclusion In a clinically and pathologically diverse sample of patients with neurodegenerative dementias, visual rating of FTP PET accurately differentiates AD from FTLD. FTP PET is not useful for the discrimination of FTLD‐tau vs. FTLD‐TDP43.