Delirium occurs commonly among hospitalized elderly patients,particularly those with dementing illness, and has a significant impact on morbidity, mortality, and cost of medical care.

Elderly patients who become delirious are at increased risk of becoming secondarily dehydrated, experiencing a serious fall, assaulting a caregiver, or having a fatal outcome. For reasons such as these, it is of critical importance that clinicians be able to recognize delirium in its overt and prodromal phases.

Even more important is the fact that delirium is a marker for emerging medical illness. If pain is conceptualized as the fifth vital sign, surely delirium should be conceptualized as the sixth. The onset of delirium always points to an underlying medical derangement. In some cases, this derangement may be life-threatening (as in the case of a cardiac dysrhythmia or so-called silent myocardial infarction), and delirium may be the first or only clue to its emergence.

Poised as it is at the interface of psychiatry and medicine, delirium invokes all of the controversies and turf battles of border conditions. Some have considered it an epiphenomenon, but arguing against this idea are the observations that delirium does not always attend particular disease states (for example, not all patients with congestive heart failure become delirious), and, when it does develop, it introduces new signs and symptoms that resolve when the episode of delirium resolves.

There has, in fact, been much speculation and little systematic research into delirium pathophysiology. There is no recognized animal model for this condition, and attempts at controlled study in humans have been confounded by associated medical illness, which is often severe.

Despite all this, a significant knowledge base on delirium has accumulated, largely through direct clinical experience. Delirium is known to be a treatable condition, even in patients with advanced dementia. As discussed in this chapter, treatment proceeds on two levels: definitive treatment of the underlying medical causes and symptomatic treatment of clinical manifestations of the delirium syndrome per se, such as hallucinations and physical aggression.


In the revised fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), the following diagnostic categories are recognized:

  • Delirium due to a general medical condition
  • Substance intoxication delirium
  • Substance-induced delirium
  • Delirium due to multiple etiologies
  • Delirium not otherwise specified

Each category has its own set of diagnostic criteria, with the first three criteria (A to C) being core criteria shared by all categories, and the fourth criterion (D) being unique to that etiology. The core criteria are as follows:

  • Disturbance of consciousness (i.e., reduced clarity of awareness of the environment) with reduced ability to focus, to sustain, or to shift attention.
  • A change in cognition (such as memory deficit, disorientation, or language disturbance) or the development of a perceptual disturbance that is not better accounted for by a preexisting, established, or evolving dementia.

The disturbance develops over a short period of time (usually hours to days) and tends to fluctuate during the course of the day.

The term acute confusional state is taken by neuropsychiatrists to be synonymous with delirium. Some neurologists refer to a hypoactive, hypoalert delirium as an acute confusional state, and reserve the term delirium for a confusional state that is comorbid with a hyperadrenergic state (as in alcohol withdrawal delirium). Theterm encephalopathy is most productively used as an alternative.