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Delirium is a medical term used to describe an acute (i.e. relatively recent) decline in attention-focus, perception, and cognition. Delirium is probably the single most common acute disorder affecting adults in general hospitals. It affects 10-20% of all hospitalized adults, and 30-40% of elderly hospitalized patients.

Delirium itself is not a disease, but rather a clinical syndrome (a set of symptoms), which result from an underlying disease or new problem with mentation. Like its components (inability to focus attention and various impairments in awareness and temporal and spacial orientation), delirium is simply the common symptomatic manifestation of early brain or mental dysfunction (for any reason).

Common usage of the term verses medical usage

In common usage, delirium is often used to refer to drowsiness and disorientation. In broader medical terminology, however, a number of other symptoms, including sudden inability of focus attention, and even (occasionally) sleeplessness and severe aggitation and irritability, are also defined as "delirium."

There are several medical definitions of delirium (including those in the DSM-IV and ICD-10). However, all include some core features.

The core features are:

  • disturbance of consciousness (that is, reduced clarity of awareness of the environment, with reduced ability to focus, sustain, or shift attention)
  • change in cognition (e.g., memory impairment) or a perceptual disturbance
  • onset of hours to days, and tendency to fluctuate.

Common features also tend to include:

  • intrusive abnormalities of awareness and affect, such as hallucinations or inappropriate emotional states.


Differential points from other processes and syndromes that cause cognitive dysfunction:

  • Delirium may be distinguished from psychosis, in which consciousness and cognition may not be impaired (however, there may be overlap, as some acute psychosis, especially with mania, is capable of producting delerium states).
  • Delirium is distinguished from dementia (chronic organic brain syndrome) which describes an "acquired" (non-congenital) and usually irreversible intellectual impairment. Dementia usually results from an identifiable degenerative brain disease (for example Alzheimer disease or Huntington's disease).
  • Delirium is distinguished by time-course from the confusion and lack of attention which result from long term learning disorders and varieties of congenital brain dysfunction. Delirium has been also referred to as 'acute confusional state' or 'acute brain syndrome'. The key word in both of these descriptions is "acute," as delirium may share many of the clinical (symptomatic) features of dementia or Attention-deficit hyperactivity disorder, with the exception of duration.


Delirium may be caused by severe physical or mental illness, or any process which interferes with the normal metabolism or function of the brain. Fever, poisons (including toxic drug reactions), brain injury, surgery, severe lack of food or water, drug and severe alcohol withdrawal are all known to cause delirium.

In addition, there is an interaction between acute and chronic symptoms of brain dysfuction; delirious states are more easily produced in people already suffering with underlying chronic brain dysfunction.

Commonly concuring mental symptoms

Confusion and disorientation

Confusion may occur with delirium, in which the sufferer loses the capacity for clear and coherent thought. It may be apparent in disorganised or incoherent speech, the inability to concentrate, or a lack of goal directed thinking.

Disorientation (another symptom of confusion) describes the loss of awareness of the surroundings, environment and context in which the person exists. Disorientation may occur in time (not knowing what time of day, day of week, month, season or year it is), place (not knowing where you are) or person (not knowing who you are).

Additional cognitive impairments which may appear in delirium

Impairments to cognition may include reduction in the function of short or long term memory, attention or problem solving.

Abnormalities of awareness and affect

Hallucinations (perceived sensory experience with the lack of an external source) or distortions of reality may occur in delirium. Commonly these are visual distortions, and can take the form of masses of small crawling creatures (particularly common in delirium tremens, caused by severe alcohol withdrawal) or distortions in size or intensity of the surrounding environment.

Strange beliefs may also be held during a delirious state, but these are not considered fixed delusions in the clinical sense as they are considered too short-lived (i.e., they are temporary delusions). Interestingly, in some cases sufferers may be left with false or delusional memories after delirium, basing their memories on the confused thinking or sensory distortion which occurred during the episode of delirium.

Abnormalities of affect which may attend the state of delirium may include many distortions to perceived or communicated emotional states. Emotional states may also fluctuate, so that a delirious person may rapidly change between, for example, terror, sadness and jocularity.


The duration of delirium is typically affected by the underlying cause. If caused by a fever, the delirious state often subsides as the severity of the fever subsides. However, it has long been suspected that in some cases delirium persists for months and that it may even be associated with permanent decrements in cognitive function. Barrough said in 1583 that if delirium resolves, it may be followed by a "loss of memory and reasoning power". Recent studies bear this out, with cognitively normal patients who suffer an episode of delirium carrying an increased risk of dementia in the years that follow. In many such cases, however, delirum undoubtedly does not have a causal nature, but merely functions as a temporary unmasking with stress, of a previously unsuspected (but well-compensated) state of minimal brain dysfunction (early dementia).


Delirium, like mental confusion, is a very general and nonspecific symptom of organ dysfunction, where the organ in question is the brain. In addition to many organic causes relating to a structural defect or a metabolic problem in the brain (analogous to hardware problems in a computer), there are also some psychiatric causes, which may also include a component of mental or emotional stress, mental disease, or other "programming" problems (analogous to software problems in a computer).

Too many to list by specific pathology, general categories of cause of delirium include:

Gross structural brain disorders

  • Head trauma (i.e., concussion, traumatic bleeding, penetrating injury, etc.)
  • Gross structural damage from brain disease (stroke, spontaneous bleeding, tumor, etc.)

Neurological disorders

General metabolic causes


Lack of essential metabolic fuels, nutrients, etc.


  • Intoxication various drugs, alcohol, anesthetics
  • Poisons (including carbon monoxide and metabolic blockade)
  • Medications including psychotropic medications

Mental illness

Psychological stressors

  • Distraction
  • Emotional shock (great fear, grief, anger, etc.)

Accounts of delirium

Sims (1995, p.31) points out a "superb detailed and lengthy description" of delirium in The Stroller's Tale from Charles Dickens' The Pickwick Papers.

Cures and treatment

Delirium is not a disease but a symptom or symptom complex, like shortness of breath, or pain. Like other symptoms, the cure and treatment relates to the underlying cause.

Further reading

  • Sims, A. (1995) Symptoms in the mind: An introduction to descriptive psychopathology. Edinburgh: Elsevier Science Ltd. ISBN 0-7020-2627-1
  • Dickens, C. (1837) The Pickwick Papers. Available for free on Project Gutenberg.
  • Burns A, Gallagley A, Byrne J. (2004) "Delirium." Journal of Neurology, Neurosurgery and Psychiatry 75 (3), 362-367.
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