Registered Nurses' Association of Ontario

Definitions of Delirium, Dementia and Depression


  • Delirium is a complex neuropsychiatric syndrome marked by an acute onset, fluctuating course, altered level of consciousness, inattention, and disorganized thinking.
  • It is described as an acute condition, usually lasting for one to seven days, it can persist for days or weeks.
  • Delirium can be thought of as acute brain failure, and may in fact indicate that the person’s brain is vulnerable and has diminishing capacity.
  • Delirium can signal a medical emergency, and its consequences may include permanent neurological effects, the development or worsening of dementia, transfer to a long-term care facility, falls, functional decline, and increased risk of death.

There are three main types of delirium:

  1. Hyperactive delirium is characterized by heightened arousal, restlessness, agitation, delusions, and/or aggressive behaviour.
  2. Hypoactive delirium is characterized by sleepiness, quieting of symptoms, and/or disinterested behaviour.
  3. Mixed delirium is characterized by alternating hyperactive and hypoactive states.


  • The Alzheimer Society of Ontario defines dementia as “a brain disorder characterized by impaired cognitive functioning that can affect learning and memory, mood and behaviour, as well as the ability to conduct daily activities and high level functions such as management of other chronic conditions.”
  • Dementia develops gradually and is progressive, but its manifestation and course can vary considerably, depending on the disease.
  • “Dementia” can be thought of as an umbrella term for a variety of diseases that create irreversible changes in the brain, including the following: Alzheimer’s disease (associated with protein plaques and tangles); vascular dementia (associated with strokes); mixed dementias (any combination of dementias, most commonly Alzheimer’s and vascular); dementia with Lewy body disease; frontotemporal dementia; and dementias associated with Creutzfeldt-Jakob disease, Parkinson’s disease, and Huntington’s disease.


  • The American Medical Directors Association has defined depression as “a spectrum of mood disorders characterized by a sustained disturbance in emotional, cognitive, behavioural, and/or somatic regulation that is associated with both significant functional impairment in daily living and often loss of one’s capacity for pleasure and enjoyment (anhedonia).”
  • Depression can be chronic, persistent, or recurrent, or it can be a reaction to events that are common in the lives of older adults, such as developing an illness, experiencing cognitive decline, losing a loved one, or being admitted to hospital or long-term care.
  • Although depression is common in older adults, it should not be considered a normal part of aging.
Older Adults
Delirium, Dementia, and Depression in Older Adults: Assessment and Care
Background Information