Regional metabolic changes in Parkinsonian patients with normal dopaminergic imaging

Dopaminergic imaging has been found to be normal in approximately 15% of parkinsonian patients enrolled in neuroprotective trials. We used ¹⁸F-fluorodeoxy glucose positron emission tomography (FDG PET) to determine the metabolic basis for this finding. We reviewed scans from 185 patients with clinical signs of Parkinson's disease (PD) who underwent ¹⁸F-fluorodopa PET imaging for diagnostic confirmation. Of this group, 27 patients (14.6%) had quantitatively normal scans; 8 of these patients were additionally scanned with FDG PET. Pattern analysis was performed on an individual scan basis to determine whether the metabolic changes were consistent with classic PD. Computer-assisted single-case assessments of the FDG PET scans of these 8 patients did not disclose patterns of regional metabolic change compatible with classical PD or an atypical parkinsonian variant. Similarly, network quantification revealed that PD-related pattern expression was not elevated in these patients as it was in an age- and duration-matched cohort with classical PD (P < 0.0001). None of these patients developed clinical signs of classical PD or of an atypical parkinsonian syndrome at a follow-up visit conducted 3 years after imaging. The results suggest that parkinsonian subjects with normal dopaminergic imaging do not have evidence of classical PD or an atypical parkinsonian syndrome.