Diagnostic Accuracy of Amyloid versus ¹⁸F-Fluorodeoxyglucose Positron Emission Tomography in Autopsy-Confirmed Dementia

Objective: The purpose of this study was to compare the diagnostic accuracy of antemortem ¹¹C-Pittsburgh compound B (PIB) and ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) versus autopsy diagnosis in a heterogenous sample of patients. Methods: One hundred one participants underwent PIB and FDG PET during life and neuropathological assessment. PET scans were visually interpreted by 3 raters blinded to clinical information. PIB PET was rated as positive or negative for cortical retention, whereas FDG scans were read as showing an Alzheimer disease (AD) or non-AD pattern. Neuropathological diagnoses were assigned using research criteria. Majority visual reads were compared to intermediate–high AD neuropathological change (ADNC). Results: One hundred one participants were included (mean age = 67.2 years, 41 females, Mini-Mental State Examination = 21.9, PET-to-autopsy interval = 4.4 years). At autopsy, 32 patients showed primary AD, 56 showed non-AD neuropathology (primarily frontotemporal lobar degeneration [FTLD]), and 13 showed mixed AD/FTLD pathology. PIB showed higher sensitivity than FDG for detecting intermediate–high ADNC (96%, 95% confidence interval [CI] = 89–100% vs 80%, 95% CI = 68–92%, p = 0.02), but equivalent specificity (86%, 95% CI = 76–95% vs 84%, 95% CI = 74–93%, p = 0.80). In patients with congruent PIB and FDG reads (77/101), combined sensitivity was 97% (95% CI = 92–100%) and specificity was 98% (95% CI = 93–100%). Nine of 24 patients with incongruent reads were found to have co-occurrence of AD and non-AD pathologies. Interpretation: In our sample enriched for younger onset cognitive impairment, PIB-PET had higher sensitivity than FDG-PET for intermediate–high ADNC, with similar specificity. When both modalities are congruent, sensitivity and specificity approach 100%, whereas mixed pathology should be considered when PIB and FDG are incongruent. ANN NEUROL 2021;89:389–401.