Delirium in the elderly 

Although delirium occurs at all ages, it is most frequently encountered in late life. This is because delirium is the result of an interaction between individual vulnerability factors (e.g. brain disease, sensory impairment) and external insults (e.g. physical illness, medication), the rates of which both increase with age. Our current concept of delirium derives principally from the florid clinical stereotype that has evolved from centuries of clinical observations on younger patients, and it may not be applicable to our historically unique ageing population. In younger adults, a major physical insult is usually necessary to precipitate delirium, which is often a dramatic disturbance. This is not the case in vulnerable elderly patients when relatively mild physical, psychological, or environmental upsets may be sufficient to bring about acute disturbances of mental functioning. These disturbances may be less obvious than in younger patients, particularly if they occur in the context of pre-existing cognitive impairment. Consequently, despite being common and problematic, delirium in elderly patients is frequently missed or misdiagnosed as dementia or depression by medical and nursing staff. This is unfortunate, because delirium is an important non-specific sign of physical illness or intoxication, and if left untreated there may be costly consequences, both for the patient and for health services.