Parkinson’s disease-related brain metabolic patterns and neurodegeneration in isolated REM sleep behavior disorder

Objective: To elucidate the role of Parkinson’s disease (PD)-related brain
metabolic patterns as a biomarker in isolated rapid-eye-movement sleep
behavior disorder (iRBD) for future disease conversion. Method: This is a
prospective cohort study consisting of 30 iRBD patients, 25 de novo PD
patients with a premorbid history of RBD, 21 long-standing PD patients on
stable treatment and 24 healthy controls. iRBD group was longitudinally
followed up. All participants underwent 18F-Fluorodeoxyglucose (FDG) PET
and were evaluated with olfaction, cognition, and the Movement disorders
society-Unified PD Rating Scale (MDS-UPDRS) at baseline. From FDG-PET
scans, we derived metabolic patterns from the long-standing PD group
(PD-RP) and de novo PD group with RBD (dnPDRBD-RP). Subsequently, we
calculated the PD-RP and dnPDRBD-RP scores in iRBD patients. We validated
the metabolic patterns in each PD group and separate iRBD cohort (n=14).
Result: The two patterns significantly correlated with each other and were
spatially overlapping yet distinct. The MDS-UPDRS motor scores
significantly correlated with PD-RP (p = 0.013) but not with dnPDRBD-RP (p
= 0.076). In contrast, dnPDRBD-RP correlated with olfaction in butanol
threshold test (p = 0.018) in iRBD subjects, but PD-RP did not (p = 0.21).
High dnPDRBD-RP in iRBD patients predicted future phenoconversion with all
cut-off ranges from 1.5 to 3 standard deviations of the control value,
whereas predictability of PD-RP was only significant in a partial range of
cut-off. Conclusion: The dnPDRBD-RP is an efficient neuroimaging biomarker
that reflects prodromal features of PD and predicts phenoconversion in
iRBD that can be applied individually.