Rapid eye movement (REM) sleep behavior disorder (RBD) is parasomnia characterized by REM sleep without atonia (RWA) and elaborate motor activity in association with dream mentation. Periodic leg movement during sleep (PLMS) is observed in a large share of patients with RBD, suggesting a common pathology: dopaminergic dysfunction. This study was undertaken to evaluate the effectiveness and mechanism of action of pramipexole, a dopamine agonist, on RBD symptoms. Fifteen patients (57-75 years

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... with RBD with a PLMS index of more than 15 events/h shown by nocturnal polysomnography were enrolled. Sleep variables, the score of severity for RBD symptoms, REM density, and PLM index were compared before and after one month or more of consecutive pramipexole treatment. Correlation analysis was conducted between the rate of change in RBD symptoms and the rate of reduction of REM density. Fourteen patients with RBD (80.0%) achieved symptomatic improvement of RBD with pramipexole treatment, which reduced REM density and PLM index during non-REM sleep despite the unchanged amount of RWA. The rate of change in RBD symptoms correlated positively with the rate of REM density reduction. Significant reduction of the PLM index was observed in non-REM sleep but not in REM sleep. Pramipexole can improve RBD symptoms, possibly because of changes in dream contents or its amount manifested as the reduction of REM density. The restricted influence of pramipexole on PLMS only during non-REM sleep suggests that other factors may affect the pathophysiology of PLMS during the REM sleep period in RBD.