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Definition: Sundowning from Encyclopedia of Alzheimer's Disease: With Directories of Research, Treatment and Care Facilities

Sundowning is a term used to describe the restlessness and agitation dementia patients experience during the late afternoon or evening hours.

Summary Article: Sundowning from The Encyclopedia of Elder Care

Sundowning (i.e., sundown syndrome) is the term that is used to describe a characteristic set of behavioral symptoms associated with cognitive and affective disorders common in older adults that occur in late afternoon, evening, or night. Sundowning is not recognized by the American Psychiatric Association (2000) in the Diagnostic and Statistical Manual of Mental Disorders (DSM), but is associated with related conditions that are part of the DSM. Sundowning occurs in cognitively impaired, demented, or institutionalized elders. Sundowning only presents in people with dementia, but not all persons with dementia experience sundowning. The name is derived from the time at which the behaviors begin, during the afternoon, evening and nighttime hours. Sundowning is a clinical diagnosis based on its features which are disruptive behaviors, confusion, disorientation, agitation, aggression, pacing, wandering, resistance to redirection, screaming, and yelling. Behaviors may be related to underlying dementia or sleep disturbances. Sundowning is always a temporal-related condition with symptoms present only later in the day. In the last decade, other clinical features have been added to include mood swings, abnormally demanding attitude, suspiciousness, and visual/auditory hallucinations occurring late in the day.

Associated terms are acute confusion, altered mental state, dementia, and delirium. Delirium is characterized by the DSM-IV-TR as disturbed consciousness (e.g., impaired environmental awareness and cognitive change including altered memory, disorientation, language disturbance) or a perceptual disturbance that cannot be accounted for by preexisting dementia. Delirium is an acute state and is always associated with mental or physical illness. In cases without mental illness, delirium is emergent and a physical or mental cause should be diagnosed as the etiology of delirium and then promptly treated, for example, urinary tract infection, pneumonia, or reaction to drugs. Delirium also may be associated with sleep–wake disturbances and the altered psychomotor behavior of sundowning. Sleep disturbances are common in persons with sundowning. Those with delirium may fall, remove their medical equipment, and vocalize by moaning, cursing, complaining, and screaming and may exhibit aggressive behavior. These behaviors have been found to be associated with a person's expression of physical pain or discomfort and emotional anguish. Nocturnal delirium is referred to as sundown syndrome.


First described in 1941 by Cameron, sundowning has received research and clinical attention, particularly because it is frustrating for caregivers, difficult to treat effectively, and recurrent. Sensory deprivation including visual limitations, but especially having inadequate exposure to light during the day is associated with confusion and sundowning, Circadian rhythm disturbances are related to sundowning such as sleep-wake cycle changes where dreams occur earlier and there are frequent, sudden wakenings and more motor activity at night. Circadian rhythms influence several physiological processes that regulate body functions and behavior. The suprachiasmatic nucleus and melatonin are involved in the pathophysiology of Alzheimer's disease (AD) and regulate circadian rhythmicity. Melatonin is produced by darkness and sleep. Circadian rhythms are observable in 24-hour cycle changes in core body temperature, hormonal secretions, red-cell production, and other physiological processes. Individuals with AD are more likely than those without AD to exhibit more activity at night and the later times of peak activity and temperature rhythms associated with sundown syndrome. Sleep disturbances, common in people with all forms of dementia, include sleep apnea, sleep fragmentation, daytime napping, and restless legs syndrome. Medications related to sundowning are antidepressants and antipsychotics, hypnotics, benzodiazepines, and may worsen sundowning symptoms.


Differential diagnosis is important when sundown syndrome is suspected. The most probable conditions causing similar signs are delirium, dementia, and depression. Acute confusion is the term preferred to describe altered cognition and behavior until delirium, dementia, and/or depression diagnoses can be established. The most frequent cause of any of these altered mental states is medication, especially antidepressants, antipsychotics, narcotics, and other drugs with psychotropic effects.

Differentiating delirium, dementia, and depression is important and a method for identifying delirium is the Confusion Assessment Method (CAM). The course of delirium fluctuates over 24 hours, whereas depression and dementia have more stable signs and are worse in the morning and during stressful situations. Delirium has a shorter course than either depression or dementia, with global rather than specific attentional disturbances, affect lability that varies from flat to excitable, impaired orientation, and incoherent speech. In depression, affect is flat and orientation is normal, with distractible attention and slowed speech. Disturbed sleep is common in both delirium and depression, but the usual pattern of daytime sleep and late wakefulness in depression is a significant indicator. In dementia, affect is usually stable and may vary from disinhibited to vegetative, with task completion muddled by the inability to plan a sequence of steps, self-monitor, and adapt to cues. The mechanics of speech are normal although there may be an inability to find or recall words.

Delirium is always related to the altered physiologic or psychological processes associated with either drug ingestion/withdrawal or general medical conditions, whereas dementia may be caused by Alzheimer's disease or by conditions such as vascular changes, Lewy body disease, Pick's disease, Huntington's disease, AIDS-related dementia, and other non-Alzheimer's pathology in the brain. Delirium is caused by diseases of body systems other than the brain, by poisons, by fluid/ electrolyte or acid/base disturbances, and by other serious, acute conditions. Infections such as urinary tract infections or pneumonia may trigger delirium in individuals with preexisting brain damage (e.g., prior strokes or dementia). Delirium is embodied by rapid changes such as from lethargy to agitation and from somnolence to euphoria with attention disruption, disorganized thinking, disorientation, and changes in sensation and perception. The multiple etiologies of delirium are described in the chapter entitled Delirium.


The most important intervention is accurate and comprehensive assessment and documentation of altered mental states so that a differential diagnosis can be made and appropriate treatment begun. When sundown syndrome is not related to an underlying medical condition, environmental interventions are appropriate. The patient's physical and social environment should be assessed for “zeitgebers,” or time providers such as lighting appropriate to the time of day and sleep needs, window shades that may be open or closed, structured meal and activity periods, suitable visitors and visiting hours, and morning and bedtime routines. Monitor and modulate noises that are intrusive and use music or other sensory salves to soothe before bedtime. Provide opportunities for daytime activity and exposure to sunlight, confine disturbing routines to early in the day, and limit access to caffeinated beverages. Melatoninis available in health food stores and may promote nighttime sleep if administered before bedtime. Of note, melatonin is not approved by the U.S. Food and Drug Administration for safety, effectiveness, or purity. Of special concern are caregivers who will need education and support in managing sundowning.

See also Delirium; Depression in Dementia; Depression Measurement Instruments; Sleep Disorders; Vascular and Lewy Body Dementias.

  • American Psychiatric Association. (2013). The diagnostic and statistical manual of mental disorders(5th ed.). American Psychiatric Publishing Arlington, VA.
Web Resources
  • ICU Delirium and Cognitive Impairment Study Group
  • National Guideline Clearinghouse
  • Society of Critical Care Medicine
  • Mary (Kelly) Dunn
    Adrianne Dill Linton
    Copyright © 2014 Springer Publishing Company

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