Reduced striatal dopamine transmission in REM sleep behavior disorder comorbid with depression.

OBJECTIVE:To investigate dopamine transmission in patients with comorbid REM sleep behavior disorder (RBD) and major depressive disorder (MDD). METHODS:This is a case-control study including 11 medicated patients with comorbid RBD and MDD (mean age 47.5 ± 8.2), 8 medicated patients with MDD only (mean age 47.9 ± 8.4), and 10 healthy participants (mean age 46.5 ± 10.6 years). They underwent clinical assessment, video-polysomnography, olfactory tests, and neuroimaging studies ((18)F-DOPA, (11)C-raclopride, and (18)F-FDG PET neuroimaging). RESULTS:Compared with the 2 control groups, patients with comorbid RBD and MDD had significantly lower (18)F-DOPA uptake at 60 minutes in the putamen and caudate after controlling for age and sex effect (p < 0.05). There were no significant differences for the (11)C-raclopride and (18)F-FDG-PET. The (18)F-DOPA uptake in putamens had significant inverse correlation with severity of RBD symptoms (p < 0.01) and REM-related tonic muscle activity (p < 0.01). The comorbid RBD and MDD group had more impairment in olfactory function. CONCLUSION:Patients with comorbid RBD and MDD had presynaptic dopamine dysfunction and impaired olfactory function. There is a distinct possibility that the development of RBD symptoms among patients with MDD may represent an early phase of α-synucleinopathy neurodegeneration instead of a merely antidepressant-induced condition.