Delirium: its historical evolution and current interpretation.

Delirium was one of the first mental disorders ever to be described, though it remains an elusive concept to this day. Historically, delirium has developed from the prototype of acute confusion with psychomotor agitation. It was thought to be caused by the withdrawal of substance dependence or severe somatic diseases accompanying by fever; however only in the 20th century, it was concluded that delirium and similar states manifest themselves as a consciousness disorder, and is not a specific state of somatic diseases. Four core features defines delirium at present: a disturbance of consciousness, a disturbance of cognition, limited course and external causation. However, these features do not include common manifestations of delirium in elderly patients with dementia; therefore the concept of delirium should be revised and corrected.