The study with that finding, “Global cognitive performance is associated with sleep efficiency measured by polysomnography in patients with Parkinson’s disease,” was published in Psychiatry and Clinical Neurosciences.
Non-motor complications associated with Parkinson’s disease, including cognitive impairment and sleep disturbances, can drastically affect patients’ quality of life.
Evidence suggests an interaction between sleep disorders and cognition. For instance, sleep after learning helps memory consolidation.
In addition, people with obstructive sleep apnea syndrome or chronic insomnia have cognitive abnormalities, which could be reversed after proper treatment of the underlying sleep disturbance.
Although there is still no consensus about whether sleep disorders are associated with cognitive dysfunction, studies suggest an association and add that rapid eye movement (REM) sleep behavioral disorder may be associated with increased risk for cognitive decline. REM is a sleep stage in which the eyes move rapidly in various directions. During sleep, the body cycles between intervals of basic states: REM sleep and non-REM sleep.
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Researchers in Brazil now examined a possible association between clinical variables, cognitive status and the presence of sleep abnormalities and symptoms in Parkinson’s patients.
Investigators performed detailed clinical and cognitive assessment in 79 patients. Participants were mostly men (61%), 51-72 years old, and a disease duration varying between 3.9 and 13.9 years.
Based on cognitive diagnosis, researchers categorized patients as those with normal cognition (29 patients), mild cognitive impairment (39 patients) or dementia (11 patients).
Within two weeks after initial medical evaluation, participants were submitted to an overnight polysomnography, meaning they had their brain waves, blood oxygen level, heart rate, breathing patterns, and eye and leg movements monitored while they were asleep.
Compared to Parkinson’s patients with normal cognition, the dementia group was older, had more severe disease, and more difficulty performing daily activities. Dementia patients also took higher daily levodopa-equivalent dose than participants without abnormalities.
Patients with dementia had lower sleep efficiency, less total sleep time and lower number of sleep state changes, in comparison to the normal cognition group.
Researchers also found an association between sleepiness, measures of obstructive sleep apnea and sleep symptoms, which were assessed by the Parkinson’s Disease Sleep Scale and the Pittsburgh Sleep Quality Index.
“Concerning sleep disorders and sleep symptoms, [there was] no significant differences between groups in the proportion of cases with obstructive sleep apnea, chronic insomnia, [REM sleep behavioral disorder] and [restless legs syndrome]. We also did not observe significant differences between scores of patients in the three groups about excessive daytime sleepiness, quality of sleep and general sleep-related symptoms. There was also no significant differences in the number of sleep disorders between the groups,” authors wrote.
There was a significant association between overall (aka “global”) cognitive performance and wakefulness and the number of sleep state changes during sleep.
“However, we did not find any other association between sleep disorders or symptoms and cognitive status or cognitive performance of patients with Parkinson’s,” researchers wrote.
The team believes the association with the number of state changes during sleep may be because Parkinson’s disease patients with dementia slept less than the other subsets and as such, had less time to change between sleep states.
“We hope that, in the near future, new prospective controlled studies, with more significant numbers of patients, could evaluate, in detail, the relationship of different variables related to sleep with cognitive functions in this specific population,” researchers concluded.