What is Delirium?

According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V), delirium is defined as a disturbance in attention and awareness that is accompanied by a change in cognition that cannot be better accounted for by a preexisting or evolving neurocognitive disorder such as dementia. This disturbance develops over a short period of time (hours to days) and tends to fluctuate during the course of the day.

Delirium is a form of acute brain dysfunction and is analogous to acute kidney injury being a form of acute kidney dysfunction. It is often precipitated by an underlying medical illness and can occur prior to any vital sign abnormalities.

Delirium is often erroneously used interchangeably with dementia. In reality, delirium and dementia are two distinct clinical entities (See Table). However, patients with dementia are highly susceptible to developing delirium. As a result, delirium and dementia often exist concurrently in the same patient.

Characteristic Delirium Dementia
Onset Acute (hours to days) Gradual (months to years)
Course Usually fluctuating Stable
Inattention* Present Usually absent
Altered level of consciousness May be present Usually absent
Disorganized thinking May be present Usually absent
Sleep-wake cycle disturbance May be present Usually absent
Perceptual disturbances May be present Usually absent
Precipitated by medical illness Almost always Rarely
Reversible Usually Rarely
Table. How delirium differs from  dementia. *Inattention is the cardinal feature of delirium.

Delirium can be further classified into three psychomotor subtypes: hypoactive, hyperactive, and mixed. Hypoactive delirium is also known as “quiet” delirium and delirious patients with this subtype can appear drowsy, somnolent, or lethargic. This delirium subtype is frequently missed by health care providers and its symptoms are often ascribed to depression or fatigue. Patients with hyperactive delirium may appear restless, anxious, agitated, or combative. Hyperactive delirium is more easily recognized by health care providers. Mixed-type delirium has characteristics of both hypoactive and hyperactive delirium. A patient with mixed-type delirium can exhibit hypoactive symptomatology at one moment and hyperactive symptomatology several hours or even seconds later. Hypoactive delirium and mixed-type delirium appear to be the predominant subtypes in older patients regardless of the clinical setting.

Watch an interview about a patient’s experience with delirium

Read more about delirium

Evidence for the diagnostic criteria of delirium: an update.

Blazer DG, van Nieuwenhuizen AO.  Curr Opin Psychiatry. 2012;25:239-243.

Read on PubMed.gov

Delirium in elderly people.

Inouye SK, Westendorp RG, Saczynski JS.  Lancet. 2014;383:911-922.

Read on PubMed.gov

Altered mental status in older patients in the emergency department.

Han JH, Wilber ST.  Clin Geriatr Med. 2013;29:101-136.

Read on PubMed.gov