What is Sundowning?
Sundowning is a clinical phenomenon in patients with dementia characterized by the emergence or worsening of neuropsychiatric symptoms—including agitation, confusion, anxiety, aggression, restlessness, and delirium—that specifically occurs in the late afternoon, early evening, or at night. 1, 2, 3
Core Clinical Features
Timing pattern: Symptoms typically manifest between late afternoon and early evening hours, with behavioral disturbances worsening as daylight fades 2, 3, 4
Symptom profile: Patients exhibit increased confusion, aggressive or disruptive behavior, wandering, restlessness, and psychotic features including delusions and hallucinations 1, 2, 3
Fluctuating course: The condition follows a predictable daily pattern, with symptoms intensifying during evening hours and often improving during morning and midday 1, 2
Prevalence: Affects approximately 1.6% to 66% of patients with dementia, with roughly one-quarter of Alzheimer's disease patients exhibiting these disruptive evening behaviors 5, 6
Underlying Pathophysiology
The biological mechanisms driving sundowning involve multiple interconnected systems:
Circadian dysfunction: Degeneration of the suprachiasmatic nucleus (SCN) in the hypothalamus—the brain's master circadian pacemaker—disrupts normal sleep-wake rhythms and leads to loss of consolidated circadian patterns 7, 3, 4
Melatonin dysregulation: Decreased melatonin production accompanies SCN degeneration, further impairing circadian synchronization 3, 4
Environmental factors: Reduced exposure to bright light and structured social/physical activities weakens the environmental time cues (zeitgebers) that normally entrain circadian rhythms 8, 7
Neurodegeneration: Progressive cognitive impairment and brain pathology in dementia directly contribute to behavioral dysregulation 2, 6
Distinction from Delirium
While sundowning shares features with delirium, key differences exist:
Delirium presents with impaired attention as the primary disturbance, acute or subacute onset, and a waxing-waning course throughout the entire day, potentially accompanied by tremor, increased muscle tone, and visual hallucinations 1
Sundowning specifically follows a predictable late-day temporal pattern in patients with established dementia, representing a circadian-mediated behavioral phenomenon rather than an acute attentional disturbance 1, 2
Clinical Significance
Caregiver burden: The unpredictable and disruptive evening behaviors create tremendous stress for caregivers and family members 2, 3, 4
Adverse outcomes: Sundowning is associated with faster cognitive decline, earlier institutionalization, and increased healthcare utilization 2, 3
Safety concerns: Evening agitation and wandering pose significant fall risks and require environmental modifications to remove dangerous objects from the bedroom 9, 8
Diagnostic Challenges
Lack of standardized criteria: No universally agreed-upon definition or specific screening tools exist for sundowning, making prevalence estimates variable 2, 3
Overlap with other conditions: Symptoms may be confused with pain, respiratory distress, medication withdrawal, or primary delirium, requiring careful differential diagnosis 1, 2, 6
Documentation requirements: Diagnosis relies on caregiver reports and observation of behavioral patterns across multiple days, ideally using sleep diaries or actigraphy 7, 5