Intrastriatal analysis of FDOPA PET scans for differentiation of Parkinsonian Disorders

Aim: L-3,4-dihydroxy-6-¹⁸F-fluorophenylalanine (FDOPA) PET allows quantification of presynaptic dopaminergic functioning in vivo. It assesses the function of nigrostriatal projection neurons, particularly dopamine release in the striatum. Previously, it was postulated that Idiopathic Parkinson’s disease (IPD) preferentially affects the posterior putamen. This study aims to investigate the potential of FDOPA PET scans to differentiate atypical parkinsonian disorders (APD), idiopathic parkinson’s disease (IPD) and healthy controls. Materials & Methods: 58 patients (28 IPD, 13 APD and 17 controls) who underwent FDOPA PET scan as part of the clinical evaluation and who were diagnosed by movement disorder specialists, were retrospectively analyzed. Average age of IPD, APD and controls was 61.0, 69.6 and 65.4 respectively. All were scanned on a Siemens HR+ camera, with injected dose of 200MBq and pretreated with carbidopa, 2.5 mg/kg orally. After spatial normalization of images in standard MNI space (Montreal Neurological Institute), predefined sets of volumes of interest (VOIs) were used to sample values from striatum and the occipital reference region. Outcome values were striatal-to-occipital ratios (SOR), intrastriatal ratios and slope of multiple in-line spherical VOIs through the striatum anterior to posterior (gradient analysis). All values were compared between groups using ANOVA test and ROC curves were calculated. Results: SOR values showed no statistically significant difference between APD and IPD patients. When analyzing intrastriatal ratios, caudate-to-putamen was found to be statistically significant when comparing APD and IPD (p<0.001; anterior putamen: 0.94±0.06 vs. 1.05±0.10; posterior putamen: 1.10±0.12 vs. 1.26±0.19, respectively). Gradient analysis also showed statistically significant differences between APD and IPD (p=0.006, 0.07±0.05 vs. 0.12±0.07). In ROC curve, separating controls from parkinsonian patients, the caudate-to-posterior putamen ratio showed the highest area under the curve (AUC=0.930), while for differentiating APD from IPD the highest AUC was the caudate-to-anterior putamen ratio (0.824). Conclusion: SOR value is currently used in clinical routine to discriminate healthy from parkinsonian patients. However, results from this study have shown that the best value for this differentiation seems to be the caudate-to-posterior putamen ratio. In addition, caudate-to-anterior putamen is capable to discriminate between atypical and idiopathic parkinsonian patients. These results are in agreement with previous publications, and support the implementation of this ratios in clinical routine. Moreover, the positive results of the gradient analysis support further exploration of this approach, and its possibilities of creating a model that combines different image measurements and/or clinical information to improve the accuracy for discriminating APD and IPD