Dementia

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.

Etiology

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.

Epidemiology

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.

Clinical Manifestations

History and Mental Status Examination
Dementia is diagnosed in the presence of multiple cognitive defects not better explained by another diagnosis. The presence of memory loss is required; in addition, one or more cognitive defects in the categories of aphasia, apraxia, agnosia, and disturbance in executive function must be present. Table 8-3 compares characteristics of dementia to those of delirium. Dementia often develops insidiously over the course of weeks to years (although it may be abrupt after head trauma or vascular insult). Individuals with dementia usually have a stable presentation over brief periods of time, although they may also have nocturnal worsening of symptoms ("sun- downing"). Memory impairment is often greatest for short-term memory. Recall of names is frequently impaired, as is recognition of familiar objects. Executive functions of organization and planning may be lost. Paranoia, hallucinations, and delusions are often present. Eventually, individuals with dementia may become mute, incontinent, and bedridden.

Differential Diagnosis

Dementia shouHbe differentiated from delirium. In addition, dementia should be differentiated from those developmental disorders (such as mental retardation) with impaired cognition. Individuals with major depression and psychosis can appear demented; they warrant a diagnosis of dementia only if their cognitive deficits cannot be fully attributed to the primary psychiatric illness.