Abnormal metabolic network activity in Parkinson's disease: test-retest reproducibility

Parkinson's disease ( PD) is associated with an abnormal pattern of regional brain function. The expression of this PD- related covariance pattern ( PDRP) has been used to assess disease progression and the response to treatment. In this study, we validated the PDRP network as a measure of parkinsonism by prospectively computing its expression ( PDRP scores) in O-15- water ((H2O)-O-15) and F-18- fluorodeoxyglucose ( FDG) positron emission tomography ( PET) scans from PD patients and healthy volunteers. The reliability of this measure was also assessed within subjects using a test - retest design in mildly affected and advanced PD patients scanned at baseline and during treatment with levodopa or deep brain stimulation ( DBS). We found that PDRP expression was significantly elevated in PD patients ( P < 0.001) relative to controls in a prospective analysis of brain scans obtained with either (H2O)-O-15 or FDG PET. A significant correlation ( R-2 = 0.61; P < 0.001) was evident between PDRP scores computed from (H2O)-O-15 and FDG images in PD subjects scanned with both tracers. Test - retest reproducibility was very high ( intraclass correlation coefficient ( ICC) > 0.92) for PDRP scores measured both within PET session and between sessions separated by up to 2 months. This high reproducibility was observed in both early stage and advanced PD patients scanned at baseline and during treatment. The within- subject variability of this measure was less than 10% for both unmedicated and treated conditions. These findings suggest that the PDRP network is a reproducible and stable descriptor of regional functional abnormalities in parkinsonism. The quantification of PDRP expression in PD patients can serve as a potential biomarker in PET intervention studies for this disorder.