Quantitative FP-CIT PET analysis of dopaminergic degeneration in isolated REM sleep behavior disorder and early Parkinson's disease.

STUDY

Objectives

Isolated REM sleep behavior disorder (iRBD) is regarded as a prodromal stage of alpha-synucleinopathies such as Parkinson's disease (PD). This study aimed to identify dopaminergic alterations in patients with iRBD using 18F-FP-CIT PET.

Methods

18F-FP-CIT PET scans from 33 healthy controls (HC), 77 patients with iRBD, and 194 patients with early PD were analyzed. Standardized uptake value ratios (SUVRs) were measured in 19 predefined brain regions, including detailed subregions of the striatum, caudate nucleus, and putamen. These quantitative markers were correlated with clinical parameters and compared with expert visual interpretations. The occurrence of phenoconversion within the iRBD cohort was investigated to evaluate the predictive value of these FP-CIT PET parameters.

Results

SUVRs exhibited a stepwise reduction (HC > iRBD > early PD) in most regions, particularly within the striatum. Putaminal asymmetry indices were elevated only in early PD, while A-P ratios differed significantly among all groups. The putaminal A-P ratio was significantly associated with depressive mood and phenoconversion, while the asymmetry index correlated with UPDRS-III motor scores. ROC and Kaplan-Meier survival analyses demonstrated that quantitative PET indices, notably the putamen SUVR and A-P ratio, effectively predicted phenoconversion within the iRBD cohort.

Conclusion

Regional quantitative 18F-FP-CIT PET reveals intermediate dopaminergic dysfunction in iRBD and highlights early posterior putamen involvement as a potential imaging marker. Quantitative PET metrics predicted phenoconversion comparably to expert visual interpretation while providing objective, continuous measures that enable individual-level risk stratification.