Brain glucose metabolism in idiopathic REM sleep behavior disorder and in Parkinson's Disease: continuum spectrum of the same disease?

Background and objective. Idiopathic REM sleep behavior disorder (iRBD) often precedes Parkinson's Disease (PD) and other alpha-synucleinopathies. The aim of the study is to investigate brain glucose metabolism of patients with RBD and PD by means of a multidimensional scaling approach, using18F-FDG-PET as a biomarker of synaptic function.
Methods. Thirty-six iRBD patients (64.1±6.5 y, 32 M), 72 PD patients and 79 controls (65.6±9.4 y, 53 M) underwent brain 18F-FDG-PET. PD patients were divided according to the absence (PD, 32 subjects; 68.4±8.5 y, 15 M) or presence (PDRBD, 40 subjects; 71.8±6.6 y, 29 M) of RBD. 18F-FDG-PET scans were used to independently discriminate subjects belonging to four categories: controls (RBD no, PD no), iRBD (RBD yes, PD no), PD (RBD no, PD yes) and PDRBD (RBD yes, PD yes).
Results. The discriminant analysis was moderately accurate in identifying the correct category. This is because the model mostly confounds iRBD and PD, thus the intermediate classes. Indeed, iRBD, PD and PDRBD were progressively located at increasing distance from controls and are ordered along a single dimension (principal coordinate analysis) indicating the presence of a single flux of variation encompassing both RBD and PD conditions.
Conclusion. Data-driven approach to brain 18F-FDG-PET showed only moderate discrimination between iRBD and PD patients, highlighting brain glucose metabolism heterogeneity among such patients. iRBD should be considered as a marker of an ongoing condition that may be picked-up in different stages across patients and thus express different brain imaging features and likely different clinical trajectories.

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Arnaldi D
Meles SK
Giuliani A
Morbelli S
Renken RJ
Janzen A
Vadasz D
the REMPET study group
the Genoa REMPET study group
Mayer G
Jonsson C
Oertel WH
Leenders KL
Nobili F
Pagani M
IOS Press, Amsterdam , Paesi Bassi
Journal of Parkinson's disease (Online) (2019).
info:cnr-pdr/source/autori:Arnaldi D, Meles SK, Giuliani A, Morbelli S, Renken RJ, Janzen A, Vadasz D, the REMPET study group, the Genoa REMPET study group, Mayer G, Jonsson C, Oertel WH, Leenders KL, Nobili F, Pagani M/titolo:Brain glucose metabolism in
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