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Overview of Delirium and Dementia

by Juebin Huang, MD, PhD

Delirium (sometimes called acute confusional state) and dementia are the most common causes of cognitive impairment, although affective disorders (eg, depression) can also disrupt cognition. Delirium and dementia are separate disorders but are sometimes difficult to distinguish. In both, cognition is disordered; however, dementia affects mainly memory, and delirium affects mainly attention.

Other specific characteristics help distinguish the 2 disorders (see Differences Between Delirium and Dementia*). Delirium is typically caused by acute illness or drug toxicity (sometimes life threatening) and is often reversible. Dementia is typically caused by anatomic changes in the brain, has slower onset, and is generally irreversible. Delirium often develops in patients with dementia. Mistaking delirium for dementia in an elderly patient—a common clinical error—must be avoided, particularly when delirium is superimposed on chronic dementia. No laboratory test can definitively establish the cause of cognitive impairment; a thorough history and physical examination as well as knowledge of baseline function are essential.

Differences Between Delirium and Dementia*

Feature

Delirium

Dementia

Onset

Sudden, with a definite beginning point

Slow and gradual, with an uncertain beginning point

Duration

Days to weeks, although it may be longer

Usually permanent

Cause

Almost always another condition (eg, infection, dehydration, use or withdrawal of certain drugs)

Usually a chronic brain disorder (eg, Alzheimer disease, Lewy body dementia, vascular dementia)

Course

Usually reversible

Slowly progressive

Effect at night

Almost always worse

Often worse

Attention

Greatly impaired

Unimpaired until dementia has become severe

Level of consciousness

Variably impaired

Unimpaired until dementia has become severe

Orientation to time and place

Varies

Impaired

Use of language

Slow, often incoherent, and inappropriate

Sometimes difficulty finding the right word

Memory

Varies

Lost, especially for recent events

Need for medical attention

Immediate

Required but less urgently

*Differences are generally true and helpful diagnostically, but exceptions are not rare. For example, traumatic brain injury occurs suddenly but may result in severe, permanent dementia; hypothyroidism may produce the slowly progressive picture of dementia but be completely reversible with treatment.

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