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Sundown syndrome

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Sundown syndrome

  • characterized by the sudden appearance of neuropsychiatric symptoms such as agitation, confusion and anxiety in a chronologic fashion, usually during late afternoon or early evening, between 4pm and 6pm (1,2,3)
  • commonly affects institutionalized or cognitively impaired individuals, but may also affect elderly inpatients (1)

  • no consensus on its operational definition
    • a descriptive term rather than a psychiatric diagnosis which occurs mainly in patients with decreased cognition or institutionalized elderly, but can also occur in hospitalized elderly in general wards
    • evidence that the syndrome affects 2.4% to 25% of patients with dementia, but it seems to affect virtually all patients with some degree of cognitive impairment and also some cognitively normal patients (1)
      • prevalence varies between 10% and 20% within institutionalized elderly (1)
    • "sundowning" broadly used to describe a set of neuropsychiatric symptoms occurring in elderly patients with or without dementia at the time of sunset, at evening, or at night
      • a wide variety of symptoms such as confusion, disorientation, anxiety, agitation, aggression, pacing, wandering, yelling and so forth (1)
        • some of these behaviors may not be specific to sundowning and can be the manifestation of dementia, delirium, Parkinson's disease, and sleep disturbances

  • equivalent to a delirium that is precipitated by diminished illumination, and can also be confused with depression or dementia
    • the difference with delirium per se is that its disruptive behavior characteristically presents at sunset or evening
      • features become prominent as natural light diminishes and increased shadows appear
      • other precipitating factors have been described, including polypharmacy changes in the environment, which may have a role in circadian rhythm (1)

  • Sundowning phenomenon is also closely related to circadian rhythm abnormalities
    • disturbances are more prominent and disabling in patients with dementia and delirium, when compared with healthy elderly
    • deterioration of circadian rhythm in these patients is probably multifactorial, caused by the neurodegenerative process, pathological changes in the retina and hypothalamic suprachiasmatic nucleus, and environmental factors (4)

  • factors that have been associated with the pathophysiology and clinical occurrence of sundowning among persons with dementia (5)

Neurobiological Factors considered to possibly contribute to "sundown syndrome"

degeneration of the suprachiasmatic nucleus

decreased melatonin production

disruption of circadian rhythms

Impaired cholinergic neurotransmission

dysregulation of the HPA axis

Medication that may have a role in development "sundown syndrome"





physological factors considered to possibly contribute to "sundown syndrome"

if the individual is tired or hungry

unmet physical or psychological needs

temporal changes in body temperature

circadian modifications of blood glucose levels

circadian changes in blood pressure

Medical Factors considered to possibly contribute to "sundown syndrome"

sleep disorders

sensory deprivation


mood disorders and fluctuations

  • diagnosis of sunset syndrome is purely clinical and involves a wide range of cognition, mood and behavior abnormalities, with temporal pattern of expression, in the late afternoon or evening


  • environmental modifications have been reported to be potentially beneficial to reduce sundown-related behavioral disorders
    • light therapy (i.e., the exposition to bright light during the afternoon/evening hours) (5)
      • been observed to produce a significant reduction of sundowning episodes and motor restless behaviors in open-label studies conducted on patients with dementia (5)
      • however a systematic review on the topic concluded that there is insufficient evidence to justify the use of bright light therapy for improving cognition, activities of daily living, sleep, challenging behaviors, and psychiatric disturbances in dementia (6)
    • other non-pharmacological strategies that have been shown to produce significant benefits in the management of neuropsychiatric symptoms (NPS) in patients with dementia (e.g., music therapy, aromatherapy, caregiver education, multisensory stimulation) may potentially be effective also in reducing sundowning (5)

  • pharmacological interventions
    • there is no definitive pharmacological treatment strategy yet defined for "sundowning"
    • evidence relating to the use of melatonin is conflicting (5)
    • antipsychotics have been frequently indicated by physicians as the most commonly prescribed class of medications to manage sundowning (5)
      • however there is limited information available in the medical literature on this particular topic, being most of RCTs focused on different NPS such as delusions, hallucinations, and agitation
      • no evidence supporting the use of benzodiazepines and other hypnotics, whose use has been instead linked with a common paradoxical increase of behavioral disturbance


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