Overview of Delirium and Dementia: Delirium and Dementia: Merck Manual Home Edition

Brain, Spinal Cord, and Nerve Disorders

Delirium and Dementia

Overview of Delirium and Dementia

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Overview of Delirium and Dementia

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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, is slowly progressive, 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 (see Biology of the Nervous System: Effects of Aging on the Nervous System).

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Comparing Delirium and Dementia
Feature	Delirium	Dementia
Development	Sudden, sometimes with a definite beginning point	Slow, with an uncertain beginning point
Cause	Almost always another condition, such as an infection, dehydration, or use or stopping of certain drugs	Usually a brain disorder, such as Alzheimer's disease, vascular dementia, or Lewy body dementia
Main early symptom	Inability to pay attention	Loss of memory, especially 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	Varies	Impaired
Effect on language	Slowed speech, often with incoherent and inappropriate language	Sometimes difficulty finding the right word
Memory	Varies	Lost, especially for recent events
Progression	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
Duration	Days to weeks, sometimes longer	Almost always permanent
Need for treatment	Immediate	Needed but less urgently
Effect of treatment	Usually reverses the losses	May slow progression but cannot reverse or cure the disorder

Comparing Delirium and Dementia

Feature

Delirium

Dementia

Development	Sudden, sometimes with a definite beginning point	Slow, with an uncertain beginning point
Cause	Almost always another condition, such as an infection, dehydration, or use or stopping of certain drugs	Usually a brain disorder, such as Alzheimer's disease, vascular dementia, or Lewy body dementia
Main early symptom	Inability to pay attention	Loss of memory, especially 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	Varies	Impaired
Effect on language	Slowed speech, often with incoherent and inappropriate language	Sometimes difficulty finding the right word
Memory	Varies	Lost, especially for recent events
Progression	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
Duration	Days to weeks, sometimes longer	Almost always permanent
Need for treatment	Immediate	Needed but less urgently
Effect of treatment	Usually reverses the losses	May slow progression but cannot reverse or cure the disorder

Last full review/revision February 2008 by Juebin Huang, MD, PhD

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