Our goal was to delineate the extra-striatal dopamine in Parkinson’s disease (PD) with and without rapid eye movement sleep behaviour disorder (RBD), while having healthy older adults as controls (HC) using in vivo PET imaging.

RBD is one of the strongest prodromal clinical predictors of PD. Molecular imaging evidence shows that PD with RBD (PD-RBD+) has a distinct striatal dopamine phenotype compared to PD without RBD (PD-RBD–) where PD-RBD+ show lower dopamine transporter activity within the caudate and putamen However, the characterization of the extra-striatal dopamine within the mesocortical and mesolimbic pathways remains unclear.

To address this knowledge gap, we recruited 15 PD-RBD+, 15 PD-RBD– and 15 HC in which they underwent PET imaging with [¹¹C]FLB-457. This technique measures [¹¹C]FLB-457 binding of D2 receptors within extra-striatal regions of interest (ROI), including the prefrontal and temporal areas. ANOVA was used to compare the binding between the three groups for each ROI; significant level was set at p<0.05 (FDR corrected).

Significant main effect was observed within the superior temporal region bilaterally; and left uncus parahippocampus. Specifically, we found that PD-RBD– binding was lower than HC in the superior temporal region bilaterally. However, the PD-RBD+ binding was found to be lower relative to HC on the right side only, and slightly higher than PD-RBD–, but this did not reach significance. Regarding the left uncus parahippocampus, both PD-RBD+ and PD-RBD– binding was lower than HC, but PD-RBD+ was slightly higher than PD-RBD–, which also did not reach significance.