In patients with Parkinson's disease (PD), abnormal activations of nociceptive brain areas and lowered pain thresholds were reported, probably reflecting a central modification of pain processing. The aim of this study was to investigate the possible correlation between the striatal and extrastriatal dopaminergic system and pain threshold in PD patients. We included 25 PD patients with various intensities of central pain (visual analog scale). Subjective pain threshold (thermotest) and a motor examination (UPDRS III) were performed. Patients underwent SPECT imaging with [123I]-FP-CIT. We analyzed the correlation between [123I]-FP-CIT binding and subjective pain threshold, using a simple linear regression model for striatal uptake and a voxel-based approach for extrastriatal uptake. The covariables were age, sex, duration of PD, and UPDRS motor score. A pain matrix mask was also used to identify clusters in relation with pain matrix. Striatal analysis revealed that [123I]-FP-CIT binding was negatively correlated with age (p = 0.02), duration of PD (p = 0.0002) and UPDRS motor score (p = 0.006), but no correlation with pain threshold was observed. The extrastriatal analysis showed a positive correlation between [123I]-FP-CIT binding and subjective heat pain threshold for the left posterior cingulate cortex (PCC) (p < 0.001) and negative correlations for the right secondary visual cortex (p < 0.001) and left insula (p < 0.001). When applying the pain matrix mask, correlations remained significant only in the left PCC and the left insula. We suggest that pain perception abnormalities in PD are not directly related to striatal dopaminergic dysfunction. Painful sensations may be related to extrastriatal monoaminergic systems.
Keywords: Central pain; Dopaminergic system; Parkinson’s disease; [123I]-FP-CIT.