β-Amyloid PET and neuropathology in dementia with Lewy bodies

Objective β-Amyloid (Aβ) pathology is common in patients with probable dementia with Lewy bodies (DLB). However, the pathologic basis and the differential diagnostic performance of Aβ PET are not established in DLB. Our objective was to investigate the pathologic correlates of 11C-Pittsburgh compound B(PiB) uptake on PET in cases with antemortem diagnosis of probable DLB or Lewy body disease (LBD) at autopsy. Methods Autopsied cases who underwent antemortem PiB-PET and were assigned a clinical diagnosis of probable DLB or LBD at autopsy were included (n = 39). The primary endpoint was pathologic diagnosis of LBD, Alzheimer disease (AD), or mixed (LBD and AD) pathology; the secondary endpoints included Thal Aβ phase and diffuse and neuritic Aβ plaques. Results Lower global cortical PiB standardized uptake value ratio (SUVr) distinguished cases with LBD from cases with AD or mixed pathology with an accuracy of 93%. Greater global cortical PiB SUVr correlated with higher Thal Aβ phase (r = 0.75, p ≤ 0.001). Voxel–based analysis demonstrated that Aβ pathology relatively spared the occipital lobes in cases with mixed pathology and LBD compared to cases with AD without LBD, in whom the entire cerebral cortex was involved. Global cortical PiB SUVr was associated primarily with the abundance of diffuse Aβ plaques in cases with LBD in a multivariable regression model. Conclusion Lower PiB uptake accurately distinguishes cases with LBD from cases with AD or mixed pathology, correlating with the Thal Aβ phase. The severity of diffuse Aβ pathology is the primary contributor to elevated PiB uptake in LBD. Classification of evidence This study provides Class III evidence that lower PiB uptake accurately distinguishes patients with LBD from those with AD or mixed pathology.