Psychiatric Times 
November 2005 Vol. XXII Issue 13
Changes in sleep are inevitable as people age, though some sleep symptoms may be due to diseases rather than aging itself (Foley et al., 1999). For example, 41% of a study sample of older adults with ≥4 medical conditions considered themselves to be fair or poor sleepers as compared to 22% with one to three conditions and only 10% of those with none (Foley et al., 2004). In this same study, poor sleep was most strongly associated with heart disease, depression, arthritis and obesity. However, even healthy seniors experience reductions in slow-wave sleep ("deep sleep") and have lower sleep efficiency with more nighttime awakenings than younger adults (Bliwise, 1993).
Patients with Alzheimer's disease (AD) may have the same sleep disturbances seen in other seniors, and, early in the course of AD, their sleep may not differ markedly from age-matched controls (Vitiello et al., 1990). In some cases, however, the sleep disturbance may be a marker for early AD. For example, investigators have reported that insomnia is an independent risk factor for cognitive decline over a three-year follow-up period (Cricco et al., 2001). Sleep-related problems generally increase as AD progresses (Moe et al., 1995). Patients with AD experience more frequent nighttime awakenings, daytime sleep increases, and both slow-wave sleep and rapid eye movement (REM) sleep are decreased (Bliwise, 1993; Prinz et al., 1982; Vitiello and Borson, 2001; Vitiello et al., 1992). Subjective sleep disturbances occur in up to 54% of patients with AD who live in the community (Carpenter et al., 1995; Chen et al., 2000; Hart et al., 2003; McCurry et al., 1999). McCurry et al. (1999) reported that 24% of caregivers report being awakened at night by the patient with AD and 40% report that patients with AD sleep more than usual.
Sleep disturbances tend to occur in patients with AD and other neuropsychiatric symptoms, such as anxiety and psychosis (Friedman et al., 1997; McCurry et al., 1999). Beyond these symptoms, disruptive nighttime behaviors secondary to confusion often develop, including nocturnal wandering, agitation, combativeness, disorientation or even delirium (Bliwise, 1993). The term sundowning is sometimes used to refer to these nighttime behaviors and erroneously used as a synonym for sleep disorder in patients with AD, but sundowning and sleep disorders are distinct syndromes. However, it is the nighttime behaviors while awake that prove distressing to patients and caregivers alike and, indeed, have been documented as the most significant contributing factor in institutionalization of patients with AD (Gaugler et al., 2000; Hope et al., 1998; Pollak and Perlick, 1991). In one study, caregivers reported that sleep disturbances were among the most distressing of all AD-related symptoms (Hart et al., 2003). In fact, of patients with AD who awaken their caregivers at night, 70% of the caregivers reported the awakenings to be moderately to severely distressing (McCurry et al., 1999).
Daytime function of patients with AD may be adversely affected by poor nighttime sleep, but there may also actually be a primary arousal problem in AD that impairs daytime alertness. Daytime sleepiness may be an early manifestation of AD, just as insomnia is. Adjusting for age and health status, older adults with daytime sleepiness are more than twice as likely to develop dementia after a three-year follow-up (Foley et al., 2001). Daytime sleepiness clearly impacts daily function in non-demented older adults (Gooneratne et al., 2003) and can be logically presumed to have at least as great an effect in patients with AD. Not surprisingly, although 38% of caregivers report moderate-to-severe distress from hypersomnia, this percentage is only half that of caregivers distressed by nighttime sleep disturbance (McCurry et al., 1999).
Alzheimer's disease sleep investigators from several centers recently proposed diagnostic criteria for defining the core sleep disturbance of AD (Yesavage et al., 2003). By defining diagnostic criteria for insomnia and hypersomnia in patients with AD, the authors provided clear diagnostic guidelines for clinical intervention and research trials. Although patients with AD may experience all the sleep disorders of old age--periodic limb movement, restless legs syndrome and sleep-related breathing disorders--the proposed diagnostic criteria specify that there is a primary sleep disturbance of AD. It is important to note, however, that the sleep disturbances seen in AD are nonspecific and can also be seen in other neurodegenerative conditions, such as vascular dementia, dementia with Lewy bodies (DLB) and Parkinson's disease. These other dementing diseases are also associated with high rates of insomnia and daytime sleepiness. Parasomnias are also more likely to occur in non-AD disorders. Some patients with dementia experience loss of muscle atonia during REM sleep that can result in dramatic motor activity and dream-enactment behavior. The syndrome, called REM behavior disorder, is not typically seen in AD, but is characteristic of DLB. Its development may even precede the dementia (Boeve et al., 1998).
Biological Mechanisms
