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The strong presence of REM sleep behavior disorder in PD

This issue of Neurology ® contains a landmark study in which an unprecedented number of patients with Parkinson disease (PD) (n = 457) at one institution underwent video-polysomnography (vPSG) for nocturnal complaints.1 A robust 46% were diagnosed with REM sleep behavior disorder (RBD) by recognized criteria,2 suggesting a strong association with PD; there is a similar association with dementia with Lewy bodies and MSA.3,4 RBD is deeply embedded within these 3 major synucleinopathies.

Limitations of this retrospective study should be noted. There is sampling bias, as patients with acute psychosis, patients with severe dementia, and noncooperative patients were excluded. The study lacks an untreated gender- and age-matched control group, and there was no randomization for subjectively disturbed vs undisturbed sleep. Diagnosis of RBD did not rely on the usual behavioral histories of patients, spouses, or other caregivers (dream-enacting behaviors, sleep-related injury, or behaviors causing sleep disruption), but rather was based exclusively on vPSG findings, the combination of REM sleep without atonia (RWA) and RBD behaviors. Consequently, the 46% RBD frequency may have been an underestimate of RBD in PD, since RBD can be diagnosed in the absence of vPSG behavioral findings if there is RWA and a history of RBD.2 The authors address this issue and provide insights into the difficulties with RBD assessment in treated patients with PD.

This study thus alerts clinicians managing patients with PD about RBD, particularly since there is increased risk for recurrent injury or death.5 In this study, RBD appeared to be of mild to moderate severity, although the retrospective design and lack of historical information limit …