PIB imaging

The development of the 11C-labelled amyloid ligand PIB as a biomarker of cortical Ap deposition has enabled in vivo assessment of amyloid burden. Although there is some variation, the overall picture is that DLB patients have PIB binding that is similar to or less pronounced than AD patients, whereas PD-D patients have similar [92] or lower [93] PIB binding than DLB patients, consistent with pathological findings. The validity of PIB binding as a marker of amyloid pathology in DLB and PD-D was supported in a study finding reduced Ap1-42 in those patients with pathological binding. The overall conclusion to date is that PD-D has a lower amyloid burden than DLB, and DLB somewhat less than AD [13, 38, 93]. PIB binding correlates with cognition in DLB but not with motor symptoms [13].


Characteristic EEG changes have been reported in patients with DLB, such as slowing of background activity and frequency variability. Two studies included both PD-D and DLB patients. In one study of patients with early and mild dementia [54], patients with DLB and PD-D had more posterior slowing and frequency variation than AD and healthy control subjects. At baseline, the changes were more common and severe in DLB than in PD-D, although at the 2-year follow-up, the changes in PD-D had become more pronounced. Interestingly, two subgroups of PD-D with and without cognitive fluctuations were identified, with EEG changes similar to the DLB group in PD-D with fluctuations group, but not in those without. In contrast, a study assessing mismatch negativity (MMN)—a component of the auditory event-related potential (ERP) considered to represent a basic automatic change detection system—found pronounced changes with reduced MMN latency and areas in PD-D, but not in DLB or AD [53]. Another study including PD, PD-D, DLB, and controls sought evidence of posterior cortical dysfunction by rhythm reactivity to eyes opening and intermittent photic stimulation (IPS) [94]. The authors found evidence for a graded posterior cortical disconnection, with decreased reactivity to IPS in PD and DLB patients and no reaction in PD-D. However, the sample was small, with only seven PD-D patients and ten DLB patients.

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