Diagnostic Accuracy of Amyloid versus FDG PET in Autopsy‐Confirmed Dementia

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Objective

To compare the diagnostic accuracy of antemortem [11C]Pittsburgh Compound B (PIB) and [18F]Flurodeoxyglucose (FDG) positron emission tomography (PET) versus autopsy diagnosis in a heterogenous sample of patients.

Methods

101 participants underwent PIB and FDG PET during life and neuropathological assessment. PET scans were visually interpreted by three raters blinded to clinical information. PIB PET was rated as positive or negative for cortical retention while FDG scans were read as showing an Alzheimer’s disease (AD) or non‐AD pattern. Neuropathological diagnoses were assigned using research criteria. Majority visual reads were compared to intermediate‐high AD Neuropathological Changes (ADNC).

Results

101 participants were included (mean age 67.2; 41 females; MMSE 21.9; PET‐to‐autopsy 4.4 years). At autopsy, 32 patients showed primary AD, 56 non‐AD neuropathology (primarily frontotemporal lobar degeneration (FTLD)) and 13 mixed AD/FTLD pathology. PIB showed higher sensitivity than FDG for detecting intermediate‐high ADNC (96% [95% confidence interval: 89‐100%] vs 80% [68‐92%], p=0.02), but equivalent specificity (86% [76‐95%] vs. 84% [74‐93%], p=0.80). In patients with congruent PIB and FDG reads (77/101), combined sensitivity was 97% [92‐100%] and specificity 98% [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%, while mixed pathology should be considered when PIB and FDG are incongruent.

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