Disordered sleep and dementia are 2 neurologic issues that are found in many of the same patients and may indeed interact. Insomnia, hypersomnia, circadian rhythm disorders, and sleep-disordered breathing are more prevalent in dementia patients than in age-matched controls. REM sleep behavior disorder can herald a synucleinopathy, such as dementia with Lewy bodies or Parkinson disease. The treatment of excessive daytime sleepiness and insomnia in dementia patients is not well described because many medications have risks that outweigh their benefits. Nevertheless, REM sleep behavior disorder has been shown in clinical trials to respond to both clonazepam and melatonin. Continuous positive airway pressure therapy can improve cognition in some cases of obstructive sleep apnea.
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• Various sleep problems such as insomnia, hypersomnia, circadian rhythm disorders, sleep-disordered breathing, and REM sleep behavior disorder are more prevalent in patients with dementia than in age-matched controls.
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• In the preclinical stages of Alzheimer disease, excessive daytime sleepiness and poor sleep efficiency appear to be associated with greater cerebral beta-amyloid burden, as measured by amyloid PET imaging. Excessive daytime sleepiness is also associated with greater cerebral Lewy body burden, as documented in autopsy studies.
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• Polysomnography is valuable as a diagnostic tool in dementia patients with sleep disorders, as relatively common sleep disorders, such as obstructive sleep apnea and REM sleep behavior disorder, are diagnosed based on the sleep study results.
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• Bright light therapy, walking with family members, and melatonin have all been used effectively to manage the sundown syndrome and poor sleep quality, which are relatively common complaints in patients with dementia with Lewy bodies, Alzheimer disease, Parkinson disease, and other dementing illnesses.
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• REM sleep behavior disorder is more common in patients with synucleinopathies such as dementia with Lewy bodies and Parkinson disease. In combination with excessive daytime sleepiness, idiopathic REM sleep behavior disorder is a predictor for mild cognitive impairment and motor dysfunction after 6 to 12 years of follow-up.
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• Melatonin and clonazepam are both effective in reducing symptoms of REM sleep behavior disorder. Melatonin can improve sleep quality in patients with mild to moderate Alzheimer disease.
Historical note and terminology
Sundown syndrome. “Sundowning,” or the nocturnal exacerbation of delirium, agitation, and aggressiveness has been recognized since the time of Hippocrates. Cameron first explored sundowning experimentally and reported that dementia patients brought into a dark room during the daytime were likely to become agitated and confused (17). The terms “sundown syndrome” or “cognitive fluctuations” are now broadly used to describe a set of neuropsychiatric symptoms that begin in the afternoon or early evening, including confusion, inattention, anxiety, pacing, wandering, and resistance to redirection (125; 67; 18; 71).
Hypersomnia. Excessive daytime sleepiness is common in the synucleinopathies, such as Parkinson disease and dementia with Lewy bodies (136), or it can be caused by sleep disordered breathing (89; 92). In Parkinson disease, hypersomnia can be related to the disease process itself, advanced age, dopaminergic medications, or to other sleep disorders such as restless legs syndrome (137; 60).
Insomnia. Chronic insomnia is the most prevalent sleep disorder in the general population (104). It is manifested by difficulty in getting to sleep, staying asleep, and in reduced quality of sleep with daytime consequences. Parkinson disease and insomnia can be aggravated by mood disorders, tremors, and nocturia (136).
REM sleep behavior disorder (RBD). This condition is either primary or secondary. Idiopathic REM sleep behavior disorder was initially described in humans in 1985 (101). It is manifested by violent behaviors, dream re-enactment, vocalizations, or involuntary leg movements during rapid eye movement (REM) or dreaming sleep. Secondary REM sleep behavior disorder has been strongly linked to a set of neurodegenerative disorders known as the synucleinopathies, which include Parkinson disease, dementia with Lewy bodies, and multiple system atrophy (03; 34; 57).
Restless legs syndrome (RLS). This condition is either primary or secondary. Patients with restless legs syndrome feel the urge to move their legs whenever they sit down or lie down. Idiopathic restless legs syndrome does not predispose patients to develop Parkinson disease or 1 of the synucleinopathies in the way that REM sleep behavior disorder does (87). Secondary restless legs syndrome occurs in 21% of Parkinson disease patients. Compared to idiopathic restless legs syndrome, it begins later in life, is less likely to be associated with a positive family history, and is less likely to be associated with a low serum ferritin level (87).
Sleep-disordered breathing. Symptoms of obstructive apnea or sleep-disordered breathing can vary from significant snoring with frequent arousals to complete airway obstruction with apneas. There has been mixed evidence in the past concerning the association of sleep-disordered breathing with dementia because it is hard to know about the directionality of the association (Plassman et al 2007; 05; 30; 28; 70). The difficulty with the older studies was their cross-sectional design. Prospective studies have documented a cause and effect relationship between sleep-disordered breathing, intermittent hypoxemia, and the risk of mild cognitive impairment and dementia (135; 89).