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Overview of Delirium and Dementia


Juebin Huang

, MD, PhD, Department of Neurology, University of Mississippi Medical Center

Last full review/revision Mar 2021| Content last modified Mar 2021
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Topic Resources

Delirium and dementia are the most common causes of mental (cognitive) dysfunction—the inability to acquire, retain, and use knowledge normally.

Although delirium and dementia may occur together, they are quite different:

  • Delirium begins suddenly, causes fluctuations in mental function, and is usually reversible.

  • Dementia begins gradually, progresses slowly, and is usually irreversible.

Also, the two disorders affect mental function differently:

  • Delirium affects mainly attention.

  • Dementia affects mainly memory.

Both delirium and dementia may occur at any age but are much more common among older people because of age-related changes in the brain.


Comparing Delirium and Dementia





Sudden, sometimes with a definite beginning point

Slow, with an uncertain beginning point


Almost always another condition, such as an infection, dehydration, or use or stopping of certain drugs

Usually a brain disorder, such as Alzheimer disease, vascular dementia, or dementia with Lewy bodies

Main early symptom

Inability to pay attention

Loss of memory, especially for recent events

Effect at night

Almost always worse

Often worse

Level of alertness (consciousness)

Impaired to varying degrees, can vary from being hyperalert to sluggish

Normal until late stages

Orientation to surroundings



Effect on language

Slowed speech, often with incoherent and inappropriate language

Sometimes difficulty finding the right word



Lost, especially for recent events


Causes variations in mental function—people are alert one moment and sluggish and drowsy the next

Slowly progresses, gradually but eventually greatly impairing all mental functions


Days to weeks, sometimes longer

Almost always permanent

Need for treatment


Needed but less urgently

Effect of treatment

Usually resolution of the symptoms

May slow progression but cannot reverse or cure the disorder

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