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, the following helps distinguish them:
Delirium affects mainly attention and awareness.
Dementia affects mainly memory and other cognitive function.
Other specific characteristics also help distinguish the two disorders (see table Differences Between Delirium and Dementia):
Delirium is typically caused by acute illness or a medication or recreational 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.
Mistaking delirium for dementia in an older patient is a common clinical error.
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 medications) | Usually a chronic brain disorder (eg, Alzheimer disease, dementia with Lewy bodies, 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 |
Effect of treatment | Usually reverses symptoms | May slow progression but cannot reverse or cure the disorder |
* 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. | ||
Although delirium and dementia are considered distinct disorders, they have a complex interrelationship. Delirium often develops in patients with dementia;it is called delirium superimposed on dementia (DSD). DSD can occur in up to 49% of patients with dementia during hospitalization. Also, patients with delirium have a higher risk of developing dementia (1).
General reference
1. Fong TG, Inouye SK:The inter-relationship between delirium and dementia: The importance of delirium prevention. Nat Rev Neurol 18 (10):579–596, 2022. doi: 10.1038/s41582-022-00698-7
