Introduction Patients with idiopathic RBD have an increased risk of developing a defined neurodegenerative disorder, the majority developing PD. Is it possible to detect features of PD in RBD, before a diagnosis of PD is established?

Methods Fifty-seven patients with polysomnography-proven idiopathic RBD and seventy-four control and drug-naïve PD subjects were recruited. All participants underwent a thorough motor and non-motor assessment, and were screened for mutations in glucocerebrosidase (GBA) genes. Visual working memory was separately assessed in 21 RBD, 15 drug-naïve PD and 21 controls using a serial order task testing both recall precision and the pattern of impairment.

Results RBD patients had increased motor and postural impairment compared to controls. Non-motor deficits (hyposmia, constipation, depression, anxiety) were similar between RBD and PD cases. Furthermore, there was a significant deficit of working memory memory recall precision in PD and RBD, with the pattern of deficit being similar in both groups.

Conclusion RBD is associated with motor and non-motor impairment often seen in early PD. The pattern of visual working memory impairment in RBD is equivalent to that observed in early PD. These results support the hypothesis that idiopathic RBD is representative of prodromal sporadic PD.