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Disturbed behaviour

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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First described more than 2500 years ago, delirium, derived from the Latin word delirare (deviate from a straight track), is an acute, fluctuating syndrome of altered attention, awareness and cognition caused by an underlying condition or event in vulnerable people (1,2,3).

  • several other names have been used in practice and in the literature to describe this condition such as - altered mental status, acute confusional state, sundowning, encephalopathy, and acute organic brain syndrome (3)
  • having delirium can result in: longer hospital stay, increased risk of dementia, increased mortality (1,4)

ICD-10 definition of delirium not induced by alcohol and other psychoactive substances:

“An aetiologically nonspecific organic cerebral syndrome characterized by concurrent disturbances of consciousness and attention, perception, thinking, memory, psychomotor behaviour, emotion, and the sleep-wake schedule. The duration is variable and the degree of severity ranges from mild to very severe” (4).

Delirium can be divided into three subtypes:

  • hperactive delirium: a subtype of delirium characterised by people who have heightened arousal and can be restless, agitated or aggressive
  • hypoactive delirium: a subtype of delirium characterised by people who become withdrawn, quiet and sleepy
  • mixed
    • hypoactive and mixed delirium can be more difficult to recognise (5)

The cause can be established within a few hours of admission in over 90% of cases and when the underlying cause has been treated then full recovery of mental function is the rule. Failure to recognise delirium and instigate the appropriate diagnostic routine is thus a serious clinical error.

It can be difficult to distinguish between delirium and dementia and some people may have both conditions. If clinical uncertainty exists over the diagnosis, the person should be managed initially for delirium


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