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Cognitive Disorders

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The cognitive disorders are delirium, dementia, and amnestic disorders. Table 8- 1 lists the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, classification of cognitive disorders.

Cognitive Disorders


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.

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).    


Dementia is characterized by the presence of memory impairment in the presence of other cognitive defects. Dementia is categorized according to its etiology (see Table 8-1). It can arise as a result of a specific disease, for example Alzheimer's disease or HIV infection; a general medical condition; or a substance-related condition; or it can have multiple etiologies. The definitive cause may not be determined until autopsy.

Generally, the etiology of dementia is brain neuronal loss that may be due to neuronal degeneration or to cell death secondary to trauma, infarction, hypoxia, infection, or hydrocephalus. Table 8-1 lists the major discrete illnesses known to produce dementia. In addition, there are a large number of general medical, substance-related, and multifactorial causes of dementia.

The prevalence of dementia of all types is about 2% to 4% after age 65, increasing with age to a prevalence of about 20% after age 85. Specific epidemiologic factors relating to disease-specific causes of dementia are listed in Table 8-4.    

Amnestic Disorders

Amnestic disorders are isolated disturbances of memory without impairment of other cognitive functions. They may be due to a general medical condition or substance related.

Amnestic disorders are caused by general medical conditions or substance use. Common general medical conditions include head trauma, hypoxia, herpes simplex encephalitis, and posterior cerebral artery infarction. Amnestic disorders often are associated with damage of the mammillary bodies, fornix, and hippocampus. Bilateral damage to these structures produces the most severe deficits. Amnestic disorders due to substance-related causes may be due to substance abuse, prescribed or over-the- counter medications, or accidental exposure to toxins. Alcohol abuse is a leading cause of substance- related amnestic disorder. Persistent alcohol use may lead to thiamine deficiency and induce Wernicke- Korsakoff's syndrome. If properly treated, the acute symptoms of ataxia, abnormal eye movements, and confusion may resolve, leaving a residual disorder called Korsakoff's psychosis induced persistent amnestic disorder).    


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