Introduction

The classical syndrome of delirium has an abrupt onset. In the elderly, it involves a rapid cognitive decline from the preexisting level of functioning (whatever that might be) involving conscious level, orientation, attention, memory and concentration. The mental state fluctuates from minute to minute or hour to hour, often worse in the evenings than mornings. There are perceptual abnormalities (illusions, hallucinations and misrecognition), affective changes (apathy, lability, irritability, autonomic arousal), persecutory or terrifying ideas, behavioral changes (hypokinesis or hyperkinesis), and motor features – ‘plucking’ and pointing are common. It is an unpleasant state with a high mortality and a high risk of adverse iatrogenic consequences. In approximately 85% of recognised cases, one or more physical causes can be identified, for example infection, intoxication with prescribed drugs, and cardiovascular, respiratory and metabolic disease. In the other 15%, psychologic factors such as removal from home, grief, depression or acute psychotic illness are sufficient to precipitate delirium. The risk of delirium appears to rise with age and underlying cerebral disease.

The clinical diagnosis of delirium involves establishing that the syndrome is present and then identifying the underlying cause or causes. Delirium is common in elderly patients on medical and psychiatric wards; estimates vary widely, depending upon the setting and the methods of assessment and diagnosis, but recent studies of acute elderly medical inpatients suggest that 10–25% are delirious (Bowler et al., 1994; Erkinjuntti et al., 1986; Rockwood, 1989; Seymour et al., 1980).