Striatal dopa and glucose metabolism in PD patients with freezing of gait.

In Parkinson's disease (PD), freezing suggests sudden and transient blocks of motor behavior during initiating or continuous repetitive movements. Its underlying pathophysiology remains unclear. The objective of this study is to compare striatal dopamine metabolism and cerebral glucose metabolism between PD patients with and without freezing of gait (FOG). A total of 10 PD patients with FOG at off and 7 PD patients without FOG underwent brain positron emission tomography with (18)[F]-6-fluoro-levodopa (FDOPA) and (18)[F]-fluordesoxyglucose (FDG). Striatum decarboxylase activity was expressed by metabolic influx constants of the striatum related to the occipital lobe (Kocc). FDG uptake in caudate and putamen was normalized to global FDG uptake. Region of interest (ROI) analysis of striatal regions was used, as well as voxel-based analysis by statistical parametric mapping (SPM). ROI analysis did not reveal differences in striatal FDOPA and FDG uptake between the groups. SPM showed lower putaminal FDOPA uptake (P = 0.05 uncorrected) with increased FDG uptake (P = 0.01 uncorrected) in freezing PD, whereas caudate uptake of the two tracers was reduced. Freezing-related cortical FDG decrease was found in (right) parietal regions. In conclusion, in freezing PD, caudate uptake of FDG and FDOPA was reduced, whereas putamen FDOPA decrease was associated with FDG increase. Right hemisphere circuitry seemed to be more affected in freezing patients.