Relationship between Delirium, Dementia and Depression

Coexistence and Overlapping Symptoms

• Delirium, dementia, and/or depression can coexist; for example, a person who has delirium may also have underlying dementia and depression, or a person with dementia may also be depressed with an underlying delirium.
• Depression is a common neuropsychiatric symptom of dementia.
• Delirium, dementia, and depression share common features with overlapping symptoms, which makes it a challenge to determine the correct diagnosis.
• Examples of errors in diagnosis:
  
  • hypoactive delirium can be mistaken for depression,
  • hyperactive delirium can be mistaken for behavioural disturbance in dementia,
  • dementia can be mistaken for depression, and depression can be mistaken for dementia.

Risk Factors and Exacerbation of Existing Conditions

Having delirium, dementia, or depression can increase a person’s risk of developing one of the other conditions, can exacerbate an existing condition, or can be a consequence of one of the other conditions. For example, studies have found the following:

• People with cognitive impairment and depression have a higher risk of developing delirium.

• Delirium may increase a person’s risk of developing dementia or may worsen the progression of dementia. 
• People with a diagnosis of dementia have a high prevalence of depressive symptoms.
• Experiencing a major episode of depression in later life may increase a person’s risk of Alzheimer’s dementia.
• Depression interacts with and may exacerbate cognitive impairment.
• Depression may contribute to behavioural symptoms (e.g., aggression) in persons with dementia.

Please note detailed information about each condition (delirium, dementia and depression) is included in the background context section of the BPG. Please access the complete guideline if you require further reading on these topics.