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Classification & external resources
ICD-10 F05.
ICD-9 293.0
DiseasesDB 29284
eMedicine med/3006 
MeSH D003693

Delirium is an acute and relatively sudden (developing over hours to days) decline in attention-focus, perception, and cognition. In medical usage it is not synonymous with drowsiness, and may occur without it. It is commonly associated with a disturbance of consciousness (eg, reduced clarity of awareness of the environment). The change in cognition (memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance, must be one that is not better accounted for by a preexisting, established, or evolving dementia. Usually the rapidly fluctuating time course of delirium is used to help in the latter distinction.[1]

Because it represents a change in cognitive function, the diagnosis cannot be made without knowledge of the affected person's baseline level of cognitive function.

Without careful assessment, delirium can easily be confused with a number of psychiatric disorders because many of the signs and symptoms are conditions present in dementia, depression, and psychosis.[2] 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).

Distressing symptoms of delirium are sometimes treated with antipsychotics, preferably those with minimal anticholinergic activity, such as haloperidol or risperidone, or else with benzodiazepines, which decrease the anxiety felt by a person who may also be disoriented, and has difficulty completing tasks. However, since these drug treatments do not address the underlying cause of delirium, and may mask changes in delirium which themselves may be helpful in assessing the patient's underlying changes in health, their use is difficult. Because delirium is a mere symptom of another problem which may be very subtle, the wisdom of treatment of the delirious patient with drugs must overcome natural skepticism, and requires a high degree of skill.


Common usage of the term versus standard 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 agitation 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., problem-solving impairment or 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 Diagnoses

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 producing delirium-like states).
  • Delirium is distinguished from dementia (chronic organic brain syndrome) which describes an "acquired" (non-congenital) and usually irreversible cognitive and psychosocial decline in function. Dementia usually results from an identifiable degenerative brain disease (for example Alzheimer disease or Huntington's disease). Once again dementia is not associated with a change in level of consciousness.
  • Delirium is distinguished from depression.
  • 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 also been referred to as 'acute confusional state' or 'acute brain syndrome'. The key word in both of these descriptions is "acute" (meaning: of recent onset), since delirium may share many of the clinical (i.e., symptomatic) features of dementia, developmental disability, or attention-deficit hyperactivity disorder, with the important exception of symptom duration.

It is a corollary of the above differential criteria that a diagnosis of delirium cannot be made without a previous assessment or knowledge of the affected person's baseline level of cognitive function.


Delirium may be caused by severe physical or mental illness, or any process which interferes with the normal metabolism or function of the brain. For example, fever, pain, poisons (including toxic drug reactions), brain injury, surgery, traumatic shock, severe lack of food or water or sleep, and even withdrawal symptoms of certain drug and alcohol dependent states, are all known to cause delirium.

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

A very common cause of delirium in elderly people is a urinary tract infection, which is easily treatable with antibiotics, reversing the delirium.

A mnemonic for the myriad causes of Delirium is: IWATCHDEATH

  • Infections (Pneumonia, Urinary Tract Infections)
  • Withdrawal (Ethanol,opiate)
  • Acute Metabolic (acidosis, renal failure, imbalances, alkalosis)
  • Trauma (acute severe pain)
  • Central nervous system pathology (epilepsy, cerebral haemorrhage)
  • Hypoxia
  • Deficiencies (vitamin B12, thiamine)
  • Endocriopathies (thyroid, parathyroid, hypopituitarism, hyper/hypoglycemia, Cushing's)
  • Acute vascular (Stroke, MI, PE, heart failure)
  • Toxins/drugs (prescribed - Tramadol, recreational)
  • Heavy metals

Commonly co-occurring mental symptoms, with a note on severity

Since delirium may occur in very many grades of severity, all symptoms may occur with varying degrees of intensity. A mild disability to focus attention may result in only a disability in solving the most complex problems. As an extreme example, a mathematician with the flu may be unable to perform creative work, but otherwise may have no difficulty with basic activities of daily living. However, as delirium becomes more severe, it disrupts other mental functions, and may be so severe that it borders on unconsciousness or a vegetative state. In the latter state, a person may be awake and immediately aware and responsive to many stimuli, and capable of coordinated movements, but unable to perform any meaningful mental processing task at all.

Inability to focus attention, confusion and disorientation

The delirium-sufferer loses the capacity for clear and coherent thought. This may be apparent in disorganised or incoherent speech, the inability to concentrate (focus attention), or in a lack of any goal-directed thinking.

Disorientation (another symptom of confusion, and usually a more severe one) describes the loss of awareness of the surroundings, environment and context in which the person exists. It may also appear with delirium, but it is not required, as noted below. Disorientation may occur in time (not knowing what time of day, day of week, month, season or year it is), place (not knowing where one is) or person (not knowing who one is).

Cognitive function may be impaired enough to make medical criteria for delirium, even if orientation is preserved. Thus, a patient who is fully aware of where they are and who they are, but cannot think because they cannot concentrate, may be medically delirious. The state of delirium most familiar to the average person is that which occurs from extremes in pain, lack of sleep, or emotional shock.

Because most high level mental skills are required for problem solving, including ability to focus attention, this ability also suffers in delirium. However, this is a secondary phenomenon, since problem-solving involves many sub-skills and basic mental abilities, any of which may be impaired in a delirious patient.

Memory formation disturbance

Impairments to cognition may include temporary reduction in the ability to form short-term or long-term memory. Difficult short-term memory tasks like ability to repeat a phone number may be continuously disrupted during a delirium, but easier short-term memory tasks like repeating single words, or remembering simple questions long enough to give an answer, may not be impaired. Reduction in formation of new long-term memory (which by definition survive withdrawal of attention), is common in delirium, because initial formation of (new) long-term memories generally requires an even higher degree of attention, than do short-term memory tasks. Since older memories are retained without need of concentration, previously formed long-term memories (i.e., those formed before the period of delirium) are usually preserved in all but the most severe cases of delirium (and when destroyed, are destroyed by the underlying brain pathology, not the delirious state per se).

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. Other instances would be inability to distinguish reality from dreams.

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, delirium 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


Lack of essential metabolic fuels, nutrients, etc.


  • Intoxication various drugs, alcohol, anesthetics
  • Sudden withdrawal of chronic drug use ("de-tox") in a person with certain types of drug addiction (e.g. alcohol, see delirium tremens, and many other sedating drugs)
  • Poisons (including carbon monoxide and metabolic blockade)
  • Medications including psychotropic medications

Mental illness per se is not a cause, as a matter of definition

Some mental illnesses, such as mania, or some types of acute psychosis, may cause a rapidly fluctuating impairment of cognitive function and ability to focus. However, they are not technically causes of delirium, since any fluctuating cognitive symptoms that occur as a result of these mental disorders are considered by definition to be due to the mental disorder itself, and to be a part of it. Thus, physical disorders can be said to produce delirium as a mental side-effect or symptom; however primary mental disorders which produce the symptom cannot be put into this category, once identified. However, such symptoms may be impossible to distinguish clinically from delirium resulting from physical disorders, if a diagnosis of an underlying mental disorder has yet to be made.

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.[3][4]

Treatment of Delirium

Delirium is not a disease, but a syndrome (i.e. collection of symptoms) indicating dysfunction of the brain, in the same way shortness of breath describes dysfunction of the respiratory system, but does not identify the disorder. Treatment of delirium is achieved by treating the underlying dysfunction cause, or in many cases, the causes (plural), as delirium is often multi-factorial.

Antipsychotics are the treatment of choice for distressing symptoms although ones with minimal anticholinergic activity, such as haloperidol or risperidone are preferable.[citation needed] Benzodiazepines are usually used in alcohol withdrawal.


  1. ^ Delirium - Cleveland Clinic. Retrieved on 2007-06-11.
  2. ^ American Family Physician, March 1, 2003 Delirium
  3. ^ Sims, Andrew (2002). Symptoms in the mind: an introduction to descriptive psychopathology. Philadelphia: W. B. Saunders. ISBN 0-7020-2627-1. 
  4. ^ Dickens, C. (1837) The Pickwick Papers. Available for free on Project Gutenberg.

Further reading

  • Burns A, Gallagley A, Byrne J (2004). "Delirium". J. Neurol. Neurosurg. Psychiatr. 75 (3): 362-7. PMID 14966146.
  • Macdonald, Alastair; Lindesay, James; Rockwood, Kenneth (2002). Delirium in old age. Oxford [Oxfordshire]: Oxford University Press. ISBN 0-19-263275-2. 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Delirium". A list of authors is available in Wikipedia.
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