First use of the term delirium is attributed to Celsus in the first century CE, but clear descriptions of the syndrome appear in the writings of Hippocrates 2500 years ago. Despite its long history, delirium remains a common but misunderstood and largely undetected disorder.
The pathophysiology of delirium is not well understood, but the significance of the disorder is as a sign of acute and often serious physical illness. Not only is it common but it carries a poor prognosis and is costly. Estimates from the United States suggest that delirium will affect more than 2.3 million older people each year, be responsible for more than 17.5 million inpatient days and cost more than $4 billion dollars (1994 dollars) each year.1
Delirium is a particularly common presentation of acute illness among older people admitted to general hospitals2–4 (Table 1) when it may be the only sign of acute illness without key localizing symptoms and signs of the underlying pathology. It is much more common in hospital than in the community. The causes of delirium are numerous.2