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 old) 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. Periodic leg movement during sleep (PLMS) is often comorbid with RBD, suggesting a common pathogenesis of the two disorders. Its frequency in RBD is higher than that seen in the normal population, especially during the REM sleep period (Fantini et al. 2002). Although two previous case series investigated the effectiveness of pramipexole on RBD symptoms (Fantini et al. 2003;Schmidt et al. 2006), these studies did not respectively examine the effect of pramipexole on PLMS during non-REM (NREM) and REM sleep periods. Moreover, the pathophysiology of PLMS in idiopathic RBD remains unsolved.Episodes of violent behavior in RBD are mostly associated with nightmares. However, no report describes the effectiveness of pramipexole for alleviating nightmares in RBD or its relation to REM density, which possibly triggers dream imagery (Ogawa et al. 2005).To elucidate the mechanism of pramipexole action on the pathogenesis of RBD, we investigated its effects on RBD symptoms, with particular attention to REM-related parameters and PLMS in this pilot study.
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