Delirium is a reversible state of global cortical dysfunction characterized by alterations in attention and cognition and produced by a definable precipitant.

Delirium is categorized by its etiology (see Table 8-1) as due to general medical conditions, substance-related, or multifactorial in origin.

Etiology
Delirium is a syndrome with many causes. Most frequently, delirium is the result of a general medical condition; substance intoxication and withdrawal also are common causes. Structural central nervous system lesions can also lead to delirium. Table 8-2 lists common general medical and substance-related causes of delirium.

Delirium is often multifactorial and may be produced by a combination of minor illnesses and minor metabolic derangements (e.g., mild anemia, mild hyponatremia, mild hypoxia, and urinary tract infection, especially in an elderly person). Common medical causes of delirium include metabolic abnormalities such as hyponatremia, hypoxia, hypercapnia, hypoglycemia, and hypercalcemia. Infectious illnesses, especially urinary tract infections, pneumonia, and meningitis, are often implicated. The common substance-induced causes of delirium are alcohol or benzodiazepine withdrawal and benzodiazepine and anticholinergic drug toxicity, although a great.number of commonly used medications, prescribed and over the counter, can produce delirium. Other conditions predisposing to delirium include old age, fractures, and preexisting dementia.

Epidemiology
The exact prevalence in the general population is unknown. Delirium occurs in 10% to 15% of general medical patients older than age 65 and is frequently seen postsurgically and in intensive care units. Delirium is equally common in males and females.

Clinical Manifestations
History and Mental Status Examination
History is critical in the diagnosis of delirium, particularly in regard to the time course of development of the delirium and to the prior existence of dementia or other psychiatric illness. Key features of delirium are

1. Disturbance of consciousness, especially attention and level of arousal;
2. Alterations in cognition, especially memory, orientation, language, and perception;
3. Development over a period of hours to days; and
4. Presence of medical or substance-related precipitants.

In addition, sleep-wake cycle disturbances and psychomotor agitation may occur. Delirium is often difficult to separate from dementia, in part because dementia is a risk factor for delirium (and thus they frequently co-occur) and in part because there is a great deal of symptom overlap, as outlined in

Table 8-3. Key differentiating factors are the time course of development of the mental status change (especially if the patient did not have a prior dementia) and the presence of a likely precipitant for the mental status change. Individuals with delirium may also display periods of complete lucidity interspersed with periods of confusion, whereas in dementia, the deficits are generally more stable. In both conditions, there may be nocturnal worsening of symptoms with increased agitation and confusion (“sundpwning”).

The diagnosis of delirium is complicated by the fact that there are no definitive tests for delirium. The workup for delirium includes a thorough history and mental status examination, a physical examination, and laboratory tests targeted at identifying general medical and substance-related causes. These should include urinalysis, complete chemistry panel, complete blood count, and oxygen saturation. Additional workup might entail chest X ray, arterial blood gas (ABG) , neuroimaging, or electroencephalogram (EEG). EEG may reveal nonspecific diffuse slowing.

The presence of a delirium is associated with a i-year mortality rate of 40% to 50%.

Differential Diagnosis
Delirium should be differentiated from dementia (although both can be present at the same time), psychotic or manic disorganization, and status complex partial epilepsy.

Management
The treatment of delirium involves keeping the patient safe from harm while addressing the delirium. In the case of delirium due to a general medical illness, the underlying illness must be treated; in substance-related delirium, treatment involves removing the offending drug (either drugs of abuse or medications) or the appropriate replacement and tapering of a cross-reacting drug to minimize withdrawal.
Delirium in the elderly is frequently multifactorial and requires correction of a multitude of medical conditions.

In addition to addressing the cause of a delirium, oral, intramuscular, or intravenous haloperidol is of great use in treating agitation. Low doses of shortacting benzodiazepines can be used sparingly. Providing the patient with a brightly lighted room with orienting cues such as names, clocks, and calendars is also useful.