Disturbed sleep, like that due to sleep apnea, significantly associates with poorer cognition in Parkinson’s disease patients, particularly in the domains of attention, executive function, and memory, a study reported.

The study, “Sleep Disturbances and Sleep Disordered Breathing Impair Cognitive Performance in Parkinson’s Disease,” was published in the journal Frontiers in Neuroscience.

Sleep problems are found in up to 90% of patients, and range from excessive daytime sleepiness and insomnia to limb movement in sleep, sleep apnea (disordered breathing), and rapid eye movement (REM) sleep behavior disorder. In recent studies, these sleep problems have been linked with greater cognitive impairment and an increased risk of dementia.

However, the association between cognitive performance and sleep quality in Parkinson’s has only been evaluated to a limited extent. This association, and whether sleep problems are a treatable cause for cognitive decline, were recently investigated by researchers in Germany.

Their study included 26 patients, mean age of 70.9, who were screened for sleeping and cognitive difficulties. Eligible participants had no depression or severe sleep apnea, atypical parkinsonian syndromes, and had not been given deep brain stimulation or medications that interfere with sleep.

In polysomnographic sleep tests — which objectively record brain waves, oxygen levels, heart rate, breathing, and movement during sleep — patients had inefficient sleep, took long periods to fall asleep, and had difficulty staying asleep. They also spent more time awake in bed, showed more limb movements while asleep, and had more fragmented sleep than is usual.

While patients with severe sleep apnea were not included, study tests found that 46% had mild to moderate sleep apnea, and 27% had a moderate form of this sleeping disorder.

Patients demonstrated problems with all tasks making up the Test of Attentional Performance (TAP), which measures such cognitive domains as attention/divided attention, alertness, executive function/response inhibition, and processing speed.

Daytime sleepiness, for example, was linked to impaired memory, worse executive function (needed to plan, focus attention, remember, and juggle multiple tasks), and poor attention and response inhibition.

Difficulty falling asleep was also significantly associated with attention deficits, while reported sleep apnea and waking up several times during the night were both associated with diminished verbal fluency.

Other factors linked with poor cognitive function included increasing age, greater motor complications, and worse scores on the Pittsburgh sleep quality index, a self-rating questionnaire assessing subjective sleep disturbances. REM disorder did not affect cognitive status.

The severity of sleep apnea appeared to correlate with worse cognitive function, particularly in the domains of attention, executive function and working memory, and memory, as well as alertness to a smaller extent.

Researchers then divided Parkinson’s patients into those with and without sleep apnea. Those with breathing stops and starts during sleep had higher blood pressure values and more respiratory events. Their sleep quality was not different from those without apnea, but their cognitive performance was significantly worse, the team noted.

In particular, people with sleep apnea had worse verbal fluency and divided attention (the ability to process information from different sources, and to carry out multiple tasks at a time).

A similar analysis comparing patients with and without REM disorder, and those with or without excessive daytime sleepiness found no differences in cognitive status between these groups.

In a final statistical analysis taking into account several confounding factors, only sleep apnea severity was significantly associated with total cognitive function scores, while sleep efficiency had a significant impact on the TAP divided attention score.

“Sleep apnea and other sleep disturbances impair cognitive performance in PD [Parkinson’s disease] and should be evaluated in routine care, and treatment options such as continuous airway pressure therapy should be considered,” the researchers wrote.