The loss of motor inhibition leads to sleep behaviors ranging from simple limb twitches to more complex integrated movements that can be violent or result in injury to either the individual or their bedmates.
[6][2] These dreams often involve screaming, shouting, laughing, crying, arm flailing, kicking, punching, choking, and jumping out of bed.
[8] As the first indication of an underlying neurodegenerative disorder or synucleinopathy, symptoms of RBD may begin years or decades before the onset of another condition.
[10] Other symptoms found in patients with RBD are reduced motor abilities, posture and gait changes, mild cognitive impairment, alterations in the sense of smell, impairments in color vision, autonomic dysfunction (orthostatic hypotension, constipation, urinary problems and sexual dysfunction), and depression.
[11] Risk factors for developing RBD are a family history of acting out dreams, prior head injury, farming, exposure to pesticides, low education level, depression, and use of antidepressants.
[12] There are a number of proposed explanations put forth by researchers to try and explain the cognitively impaired phenotype of PD that is linked to RBD.
However, there is not much research support for this idea and there is a lack of association between different sleep disorders, such as insomnia, and cognitive decline in PD.
This difference is seen particularly in brain structures like the basal forebrain, an area implicated in both cognition and the regulation of REM sleep and muscle tone through interactions with brainstem nuclei.
[14] This hypothesis is supported by the amelioration of RBD symptoms through the use of acetylcholinesterase inhibitors, drugs which lead to an increase in cholinergic neurotransmitters in the brain.
[14] A reduction in grey matter volume and cortical thinning, especially in the frontal cortex and inferior parietal lobe of the brain, have also been proposed as the potential cause of PDRBD.
The left insular cortex in particular has shown much greater levels of cortical thinning in PDRBD compared to PD without RBD.
An area of the brain considered an ‘integrating hub’ of higher-level cognitive processes with social-emotional and sensorimotor functioning.
[1][17] The REM Sleep Behavior Disorder Single-Question Screen offers diagnostic sensitivity and specificity in the absence of polysomnography with one question:[2] "Have you ever been told, or suspected yourself, that you seem to 'act out your dreams' while asleep (for example, punching, flailing your arms in the air, making running movements, etc.)?
On average 75%-80% of patients with PDRBD go onto receive a diagnosis of MCI, and then a further 30% develop some form of dementia, within 15–20 years of PD onset.
[23] However, the existence of a unique and specific cognitively impaired profile among PD patients with RBD is still deemed controversial.
[2] In addition to medication, it is wise to secure the sleeper's environment by removing potentially dangerous objects from the bedroom and either place a cushion around the bed or move the mattress to the floor for added protection against injuries.
[2] In extreme cases, an affected individual has slept in a sleeping bag zipped up to their neck, wearing mittens so they cannot unzip it until they awake.
The disorders most strongly associated with RBD are the synucleinopathies, particularly Parkinson's disease, dementia with Lewy bodies, and to a lesser extent, multiple system atrophy.
Hence, this link could provide an important window of opportunity in the implementation of therapies and treatments, that could prevent or slow the onset of PD.