Objective: In the present study, we tried to elucidate if the occipital hypometabolism detected by [(18) F]-fluoro-d-glucose (FDG) positron emission tomography (PET) scan in patients with idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD)  predicts Parkinson’s disease (PD).

Background: Idiopathic RBD could be a prodromal state of PD. FDG-PET is known to show occipital hypometabolism in patients with both iRBD and PD.

Methods: We enrolled 10 patients with non-demented iRBD (6men and 4 women) in the present study, and followed up their clinical symptoms for more than 5 years. At the beginning of the study, all the patients underwent FDG-PET scanｓ as well as mini-mental state examinations (MMSE), and neurological examinations to detect Parkinsonism. After the baseline evaluations, Parkinsonism of the patients were checked every one to three months until the patients’ symptoms fulfil the UK brain bank criteria for PD. MMSE score was also checked every one year. Results of FDG-PET scan were compared with those of 18 patients with idiopathic PD (12 men and 6 women).

Results: There was no difference of age between iRBD and PD patients. Occipital hypometabolism was detected in both groups. The degree of hypometabolism, however, was more severe in patients with PD. One patient with iRBD showed no occipital hypometabolism. During the follow-up period, one iRBD patients dropped out because of the move occurred 22 months after the FDG-PET study. Six out of 9 remaining iRBD patients developed PD during the follow-up period. Latency to develop PD after FDG-PET ranges between 16 and 96 months. Three patients showed no parkinsonism during follow-up period ranging from 66 to 121 months. One patient who did not show occipital hypometabolism remained iRBD for 121 months. Whereas, one patient who showed the highest score on occipital hypometabolism among iRBD patients developed PD in 31 months. MMSE score remained more than 24 in all the iRBD patients during the follow-up periods.

Conclusions: Patients with iRBD show occipital hypometabolism on FDG-PET, although the degree is smaller than that in patients with PD. Marked hypometabolism on FDG-PET is likely to predict the early progression to PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/marked-occipital-hypometabolism-on-fdg-pet-in-patients-with-idiopathic-rbd-may-predict-parkinsons-disease/