Is It Delirium or Dementia?
Distinguishing Between Two Commonly-Used Terms is Important
May 15, 2009
Disruption of normal thought patterns can occur in a variety of settings: Trauma, depression and other affective disorders, psychotic disorders, drug or alcohol use, metabolic disease, or chronic brain disorders (e.g., Alzheimer’s disease) are among the conditions that provoke abnormal cognitive states.
Two of the most common causes of cognitive impairment are dementia and delirium. These terms are often incorrectly used interchangeably.
Even among medical professionals, the term “demented” is sometimes inappropriately used to describe people who are unfocused, confused, or inattentive. Strictly speaking, dementia is a disorder that mainly affects memory; delirium is the term that is more properly applied to individuals with disorders of attention.
Although the two conditions can overlap, the distinction between dementia and delirium is more than academic; the underlying causes of delirium are often treatable, and the condition is usually transient and reversible. Conversely, dementia is often progressive and irreversible.
Unfortunately, distinguishing between delirium and dementia is not always easy, and some conditions that cause dementia are, indeed, reversible (e.g., major depression or hypothyroidism can cause dementia, and treating the underlying conditions leads to resolution of the dementia).
For the layperson who may encounter cognitive impairment in a family member, understanding the differences between dementia and delirium will help to solidify expectations, assist with caring for the affected person, and possibly guide the hands of treating physicians.
Important Differences Between Delirium and Dementia
- Onset: Delirium is usually sudden in onset, with a definable starting point. Dementia is gradual in onset, with an ill-defined starting point
- Duration: Delirium lasts days to weeks; dementia tends to be permanent (unless there is a treatable cause)
- Causes: Delirium nearly always arises from another condition: medications, substance abuse or withdrawal, infection, dehydration, etc. Dementia usually results from a chronic brain disorder (Alzheimer’s dementia, cerebrovascular disease, etc.)
- Course and prognosis: Delirium is typically reversible, while dementia is usually progressive and permanent
- Effect on attention: Delirium greatly impairs one’s ability to focus and stay on task; demented persons can usually attend to tasks until their condition is far advanced
- Effect on memory: Delirious patients demonstrate variable levels of recall; by definition, demented persons exhibit memory impairment (especially for recent events)
- Consciousness level: Varies from sluggish to hyper-alert in delirium; demented individuals show little change until condition is severe
- Orientation to person, time, and place: Variable in delirium; dementia nearly always impairs orientation in at least one sphere
- Language skills: Delirious individuals may be incoherent or use words inappropriately; demented people often search for “the right word”
- Effect of nightfall: Delirium almost always grows worse at night (“sun-downing”); effect of nightfall is variable in dementia
- Need for medical intervention: Since some underlying causes of delirium can be fatal, these patients require immediate attention; dementia requires ongoing, less urgent medical care
(From The Merck Manual, 18th Edition. Delirium and Dementia. 2006:1808-1815)
The terms “delirium” and “dementia” describe different categories of cognitive impairment. Whereas delirium is usually acute, transient, and reversible, dementia is most commonly gradual in onset, progressive, and permanent.
Distinguishing between these two terms has important therapeutic and prognostic ramifications.
