Cognitive dysfunction and REM sleep behavior disorder: Key findings in the literature and preliminary longitudinal findings

• Cognitive deficits similar to those seen in synucleinopathies are detectable in iRBD.
• Cognitive dysfunction progresses in 47% of iRBD patients over a 3-year period.
• It has not been proved that cognitive deficits are predictive of parkinsonism in iRBD.
• There is evidence that RBD is associated with an increased risk of dementia in PD.

A considerable proportion of subjects initially diagnosed with idiopathic REM sleep behavior disorder (iRBD) are reported to convert to a neurodegenerative disorder, mainly synucleinopathies.It is unclear whether cognitive deficits in iRBD represent an associated feature or a marker predictive of subsequent development of a synucleinopathy.Cross-sectional studies indicate that a proportion of iRBD patients show cognitive deficits similar to those typically found in patients with synucleinopathies.The available longitudinal data suggest that cognitive dysfunction in iRBD tends to progress over time, with this progression probably being underpinned by a neurodegenerative process.Furthermore, within the framework of Parkinson's disease, RBD has been shown to be a risk factor for progressive cognitive decline even advancing to dementia.This paper addresses the multifaceted issue of cognitive dysfunction in RBD. Taking into account some key literature findings and preliminary longitudinal observations of our own, it shows that cognitive deterioration, mainly involving visuospatial abilities (learning as a stable deficit and copying as an evolving deficit), non-verbal logic, attention and executive functions can be observed in iRBD follow-up, suggesting an underlying evolving degenerative process.Large cohort studies with more prolonged follow-ups and greater methodological uniformity are needed to provide more reliable and robust findings.