Corticostriatal covariance patterns of 6-[18F]fluoro-L-dopa and [18F]fluorodeoxyglucose PET in Parkinson's disease

6-[F-18]fluoro-L-dopa (FDOPA) is a common presynaptic dopaminergic tracer used in examinations by positron emission tomography (PET) for patients with Parkinson's disease (PD). The distinct metabolic covariance pattern in the uptake of [F-18]fluorodeoxyglucose (FDG) can also be used to investigate PD pathology. Although the two tracers are widely used in PD research and clinical assessment, no thorough comparative studies of the tracers have been made. In this study, 25 PD patients were examined with FDOPA and FDG to investigate relationships and clinical correlates of metabolic and monoaminergic function in the Parkinsonian brain. A VOI (volume-of-interest) analysis was achieved by 3D spatial normalisation and fixed VOI-sets. The hemisphere ipsi- and contralateral to the predominant symptoms of PD was identified in each data set, and data across subjects were related using that laterality, rather than body side. Regional covariance patterns for FDOPA and FDG were derived from principal component analysis (PCA). The results demonstrated hemispheric asymmetries and sex-differences in the striatal FDOPA uptake, which were not seen with FDG. In addition, the PCA analysis identified a positive relationship between a major component in FDOPA uptake (associated with the striatal uptake) and an FDG component, which had positive loadings in the thalamus and the cerebellum. The subject scores for these components correlated positively, and both had a negative association with the clinical severity of the disease. The specific extrastriatal FDG covariance pattern contained the thalamus and the cerebellum, components of the previously reported PD related pattern, but not the striatum. The network correlated with both the severity of clinical symptoms of PD and the severity of nigrostriatal dopaminergic hypofunction. The results indicate that FDG PET, when combined with multivariate network analysis at group-level, can be used as an indicator of PD severity.