Delirium, also sometimes known as acute confusional state, acute organic reaction, acute brain syndrome, or toxic-metabolic encephalopathy, is a neurobehavioral syndrome of which the cardinal feature is a deficit of attention, the ability to focus on specific stimuli. Diagnostic criteria also require a concurrent alteration in level of awareness, which may range from lethargy to hypervigilance, although delirium is not primarily a disorder of arousal or alertness (cf. coma, stupor, obtundation). Other features commonly observed in delirium include:

  • Impaired cognitive function: disorientation in time and place
  • Perceptual disorders: illusions, hallucinations
  • Behavioral disturbances: agitation, restlessness, aggression, wandering, which may occur as a consequence of perceptual problems;
  • Language: rambling incoherent speech, logorrhea
  • Altered sleep-wake cycle: "sundowning" (restlessness and confusion at night)
  • Tendency to marked fluctuations in alertness/activity, with occasional lucid intervals
  • Delusions: often persecutory.

Hence this abnormal mental state shows considerable clinical heterogeneity. Subtypes or variants are described, one characterized by hyperactivity ("agitated"), the other by withdrawal and apathy ("quiet").

The course of delirium is usually brief (seldom more than a few days, often only hours). On recovery the patient may have no recollection of events, although islands of recall may be preserved, corresponding with lucid intervals (a useful, if retrospective, diagnostic feature).

Delirium is often contrasted with dementia, a "chronic brain syndrome", in which attention is relatively preserved, the onset is insidious rather than acute, the course is stable over the day rather than fluctuating, and which generally lasts months to years. However, it should be noted that in the elderly delirium is often superimposed on dementia, which is a predisposing factor for the development of delirium, perhaps reflecting impaired cerebral reserve.

The pathophysiology of delirium is not well understood. Risk factors for the development of delirium may be categorized as either predisposing or precipitating.

  • Predisposing factors include:
    • Age: frailty, physiological age rather than chronological
    • Sex: men > women
    • Neurological illness: dementia
    • Burden of comorbidity; dehydration
    • Drugs: especially anticholinergic medication
    • Primary sensory impairment (hearing, vision)
  • Precipitating factors include:
    • Drugs/toxins: benzodiazepines, opiates
    • Alcohol, especially withdrawal from, as in delirium tremens Intercurrent illness:
      • Infection: primary CNS (encephalitis, meningitis), or systemic (urinary tract, chest, septicemia)
      • Metabolic: hypoxia, hypo-/hyperglycemia, hepatic failure, uremia, porphyria
      • CNS disorders: head injury, cerebrovascular disease, epilepsy (e.g., some forms of status), inflammatory disorders (e.g., collagen vascular disease)
    • Iatrogenic events: surgery (especially cardiac, orthopedic)

These precipitating factors merit treatment in their own right, and investigations should be tailored to identify these etiological factors. The EEG may show nonspecific slowing in delirium, the degree of which is said to correlate with the degree of impairment, and reverses with resolution of delirium.

It is suggested that optimal nursing of delirious patients should aim at environmental modulation to avoid both underand over-stimulation; a side room is probably best (if possible).

Drug treatment is not mandatory, the evidence base for pharmacotherapy is slim. However, if the patient poses a risk to him/herself, other patients, or staff which cannot be addressed by other means, regular low dose haloperidol may be used, probably in preference to atypical neuroleptics, benzodiazepines (lorazepam), or cholinesterase inhibitors.



Ashton H. Delirium and hallucinations. In: Perry E, Ashton H, Young A (eds.). Neurochemistry of consciousness: neurotransmitters in mind. Amsterdam: John Benjamins, 2002: 181-203
Burns A, Gallagley A, Byrne J. Delirium. Journal of Neurology,Neurosurgery and Psychiatry 2004; 75: 362-367
Larner AJ. Delirium: diagnosis, aetiopathogenesis and treatment. Advances in Clinical Neuroscience & Rehabilitation 2004; 4(2): 28-29 Lindesay J, Rockwood K, Macdonald A (eds.). Delirium in old age. Oxford: OUP, 2003
Nayeem K, O’Keeffe ST. Delirium. Clinical Medicine 2003; 3: 412-415


Cross References

Agraphia; Attention; Coma; Delusion; Dementia; Hallucination; Illusion; Logorrhea; Obtundation; Stupor; "Sundowning"