Delirium

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