Detection of Striatal Amyloid Plaques with [18F]flutemetamol: Validation with Postmortem Histopathology

Amyloid imaging is limited by an inconsistent relationship between cerebral cortex amyloid- β (Aβ) plaques and dementia. Autopsy studies suggest that Aβ plaques first appear in the cerebral cortex while subcortical plaques are present only later in the disease course. The presence of abundant plaques in both cortex and striatum is more strongly correlated with the presence of dementia than cortical Aβ plaques alone. Additionally, detection of striatal plaques may allow, for the first time, pathology-based clinical staging of AD. Striatal plaques are reportedly identifiable by amyloid imaging but the accuracy and reliability of striatal amyloid imaging has never been tested against postmortem histopathology. To determine this, we correlated the presence of histopathologically-demonstrated striatal Aβ deposits with a visually positive panel consensus decision of a positive [18F]flutemetamol striatal PET signal in 68 subjects that later came to autopsy. The sensitivity of [18F]flutemetamol PET striatal amyloid imaging, for several defined density levels of histological striatal Aβ deposits, ranged between 69% and 87% while the specificity ranged between 96% and 100%. Sensitivity increased with higher histological density thresholds while the reverse was found for specificity. In general, as compared with PET alone, PET with CT had slightly higher sensitivities but slightly lower specificities. In conclusion, amyloid imaging of the striatum with [18F]flutemetamol PET has reasonable accuracy for the detection of histologically-demonstrated striatal Aβ plaques when present at moderate or frequent densities. Amyloid imaging of the cerebral cortex and striatum together may allow for a more accurate clinicopathological diagnosis of AD and enable pathology-based clinical staging of AD.