Delirium Delirium Delirium is an acute, transient, usually reversible, fluctuating disturbance in attention, cognition, and consciousness level. Causes include almost any disorder or drug. Diagnosis is clinical... read more (sometimes called acute confusional state) and dementia Dementia Dementia is chronic, global, usually irreversible deterioration of cognition. Diagnosis is clinical; laboratory and imaging tests are usually used to identify treatable causes. Treatment is... read more 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.
Dementia affects mainly memory.
Other specific characteristics also help distinguish the two disorders (see table Differences Between Delirium and Dementia 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 older 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.
