Objective: Imaging of regional cerebral glucose metabolism with PET and striatal dopamine D2/D3 receptors (D2R) with SPECT improves the differential diagnosis of parkinsonism. We prospectively investigated 1) the diagnostic merits of these approaches in differentiating between Lewy body diseases (LBD; majority Parkinson disease [PD]) and atypical parkinsonian syndromes (APS); 2) the diagnostic value of [¹⁸F]fluorodeoxyglucose (FDG)-PET to differentiate among APS subgroups.

Methods: Ninety-five of 107 consecutive patients with clinically suspected APS referred for imaging were recruited. [¹⁸F]FDG-PET scans were analyzed by visual assessment (including individual voxel-based statistical maps). Based on a priori defined disease-specific patterns, patients with putative APS were differentiated from LBD (first level) and allocated to the subgroups multiple system atrophy (MSA), progressive supranuclear palsy (PSP), or corticobasal degeneration (CBD) (second level). [¹²³I] iodobenzamide (IBZM)-SPECT datasets were subjected to an observer-independent regions-of-interest analysis to assess striatal D2R availability. Movement disorder specialists made final clinical diagnoses after a median follow-up time of 12 months.

Results: Seventy-eight patients with clinically verified APS (n = 44) or LBD (n = 34) were included in the statistical analysis. The area under the receiver operating characteristic curve for discrimination between APS and LBD was significantly larger for [¹⁸F]FDG-PET (0.94) than for [¹²³I]IBZM-SPECT (0.74; p = 0.0006). Sensitivity/specificity of [¹⁸F]FDG-PET for diagnosing APS was 86%/91%, respectively. Sensitivity/specificity of [¹⁸F]FDG-PET in identifying APS subgroups was 77%/97% for MSA, 74%/95% for PSP, and 75%/92% for CBD.

Conclusions: The diagnostic accuracy of [¹⁸F]FDG-PET for discriminating LBD from APS is considerably higher than for [¹²³I]IBZM-SPECT. [¹⁸F]FDG-PET reliably differentiates APS subgroups.