Table 1.

Comparative features of delirium and dementia

Feature	Delirium	Dementia
Onset	Abrupt, though initial loss of mental clarity may be subtle	Insidious and progressive
Duration	Hours to days (though can be prolonged)	Months to years
Attention	Reduced ability to focus, sustain, or shift attention is a hallmark feature, occurring early in presentation	Normal unless severe dementia
Consciousness (awareness of the environment)	Fluctuating (making assessment at multiple timepoints necessary), reduced level of consciousness and impaired orientation	Generally intact
Speech	Incoherent, disorganised; distractible in conversation	Ordered, may develop anomia or aphasia
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 process (e.g. beta-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 that there is substantial overlap between these syndromes; they may coexist in an individual patient.