Table 1.

Features of delirium and dementia

Feature	Delirium	Dementia
Features	Inattention and impairment of immediate memory	Memory impairments range from mild to severe; multiple cognitive domains also impaired
Onset	Acute and episodic, though initial loss of mental clarity may be subtle	Insidious and progressive/gradual
Duration	Hours to weeks (though can be prolonged)	Months to years
Time course	Fluctuating (must assess for symptoms at multiple time points); may be worse at night and on waking	Chronic, progressive
Attention	Impaired ability to focus, sustain, or shift attention is an essential and characteristic feature	Normal in early stages of dementia
Consciousness (awareness of the environment)	Altered level of consciousness and impaired orientation	Generally intact
Reversibility	Usually	No
Speech and thought	Incoherent Disorganized, disconnected “flight of ideas” May include delusions	Word-finding difficulties Difficulty with abstract thinking
Perception	Distorted—illusions, delusions, and/or hallucinations (often visual, tactile, or poorly formed)	Delusions of theft, persecution. Hallucinations uncommon (auditory, distinct)
Psychomotor changes	Yes, frequent	Yes, inconsistent
Agitation	Occurs with delirium symptoms, throughout the day	Sundowning may occur
Sleep-wake cycle	Often reversed	Maybe fragmented, but circadian rhythmicity retained
Other features	Caused by underlying medical condition, substance intoxication, or medication side effect; hyperactive, hypoactive, and mixed forms of psychomotor disturbance are possible; disruption in sleep duration and architecture; perceptual disturbances	Caused by underlying neurological processes (e.g., β-amyloid plaque accumulation in Alzheimer’s disease), with symptoms varying depending on underlying pathologies (e.g., fluctuations in cognition are a feature of Lewy body dementia)

Note: These syndromes have substantial clinical overlap and patients can have delirium superimposed on dementia.