The Value of the Dopamine D2/3 Receptor Ligand 18F-Desmethoxyfallypride for the Differentiation of Idiopathic and Nonidiopathic Parkinsonian Syndromes

We evaluated the utility of the selective dopamine D-2/3 receptor ligand F-18-desmethoxyfallypride (F-18-DMFP) for the differential diagnosis of patients with idiopathic parkinsonian syndrome (IPS) and nonidiopathic parkinsonian syndrome (non-IPS). On the basis of the superior sensitivity of PET, we hypothesized that F-18-DMFP should have properties for the differential diagnosis of these syndromes superior to what has been reported for the more conventional SPECT procedures. Methods: A series of 81 patients with parkinsonism (26 women, 55 men; mean age +/- SD, 68 +/- 11 y) were included in this retrospective analysis. A 30-min F-18-DMFP PET recording was acquired starting 1 h after injection of the tracer (180-200 MBq, intravenously). The specific binding (SB) in divisions of the striatum was calculated relative to the occipital cortex using an observer-independent semiautomatic volume-of-interest-based technique. The optimal SB threshold was defined by means of receiver-operating-characteristic analysis, which was also used for the evaluation of the diagnostic performance of SB, ratios between striatal sub-regions, and absolute asymmetries in SB. Results: Significant differences (P < 0.001) were found in striatal SB between IPS and non-IPS, most notably in the posterior putamen, for which the diagnostic power for discrimination of IPS and non-IPS was the highest (sensitivity, 87%; specificity, 96%; and accuracy, 91%). A further gain of diagnostic power (sensitivity, 92%; specificity, 96%; and accuracy, 94%) was obtained through discriminant analysis combining 3 parameters: SB of the posterior putamen, the posterior-to-anterior putamen ratio, and the posterior putamen-to-caudate ratio. Conclusion: F-18-DMFP PET is useful for the differential diagnosis of IPS and non-IPS in patients with parkinsonism. The findings are consistent with relative sparing of D-2/3 receptors in the dopamine-denervated putamen of IPS patients, in contrast to a more substantial loss of striatal dopamine receptors in non-IPS patients. The PET procedure for this differential diagnosis was superior to the reported experience with I-123-iodobenzamide SPECT.