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.

What is Delirium?

Watch an interview about a patient’s experience with delirium

Read more about delirium

Evidence for the diagnostic criteria of delirium: an update.

Delirium in elderly people.

Altered mental status in older patients in the emergency department.