Table 1.

Features of delirium and dementia

Feature	Delirium	Dementia due to Alzheimer disease	Frontotemporal lobe dementia	Diffuse Lewy body disease	Vascular dementia
Descriptive features	Inattention, impairment of immediate memory	Memory impairments, plus impairments in multiple other cognitive domains	Behavioural disorder, mental rigidity, distractibility	Fluctuating cognition with variations in attention and alertness	Abrupt deterioration or stepwise progression of cognitive deficits; mood and personality changes
Onset	Acute, episodic	Insidious	Insidious	Insidious	Insidious, abrupt or stepwise
Duration	Hours to months	Months to years	Months to years	Months to years	Months to years
Course	Fluctuating, might be worse at night and on waking	Chronic, progressive	Chronic, progressive	Chronic, progressive	Chronic, progressive
Alertness	Altered	Normal	Normal	Fluctuates	Normal
Reversibility	Usually	No	No	No	No
Attention	Impaired by definition	Usually, normal, but might be impaired in later stages	Might be persistently impaired and early feature	Fluctuates	Might be persistently impaired and early feature
Orientation	Fluctuates	Not oriented	Typically intact	Variable	Variable
Speech	Incoherent speech	Word-finding difficulties	Altered speech output; stereotypy of speech; echolalia; perseveration; mutism	Hypophonic speech	–
Thought	Disorganized and disconnected thoughts, for example, ‘flight of ideas’	Difficulty with abstract thinking	Poor judgement; impulsivity	–	Abnormal executive function, including mental rigidity and poor insight and judgment
Perception	Distorted: illusions, delusions and/or hallucinations (often visual, tactile or poorly formed)	Delusions of theft or persecution, more common in later stages; hallucinations (auditory, distinct) uncommon	Delusions might be paranoid, religious or bizarre in nature	Visual hallucinations are recurrent and typically well-formed and detailed (that is, animals or children); delusions are common	Delusions more common in later stages
Psychomotor changes	Frequent	Inconsistent	Hyperorality; utilization behaviour	Parkinsonism	Psychomotor retardation
Agitation	Occurs with delirium symptoms, throughout the day	Might occur with sundowning or when resisting activities of daily living	Common	Variable	Variable
Sleep–wake cycle	Often reversed	Might be fragmented but circadian rhythmicity retained	Severely fragmented	REM sleep behaviour disorder	Sleep disturbances are common