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.

A critical component of differential diagnosis in dementia is to distinguish pseudodementia associated with depression. Although there are many precise criteria for separating the two disorders, neuropsychological testing may be needed to make an accurate diagnosis. In pseudodementia, mood symptoms are prominent and patients may complain extensively of memory impairment. They characteristically give “I don’t know” answers to mental status examination queries but may answer correctly if pressed. Memory is intact with rehearsal in pseudo-dementia, but not in dementia.

Management
Dementia from reversible, or treatable, causes should be managed first by treating the underlying cause of the dementia; rehabilitation may be required for residual deficits. Reversible (or partially reversible) causes of dementia include normal pressure hydrocephalus; neurosyphilis; HIV infection; and thiamine, folate, vitamin BI2, and niacin deficiencies. Vascular dementias may not be reversible, but their progress can be halted in some cases. Nonreversible dementias are usually managed by placing the patient in a safe environment and by medications targeted at associated symptoms. Tacrine, an acetylcholinesterase inhibitor, has some effIcacy in treating memory loss in dementia of the Alzheimer’s type. High-potency antipsychotics (in low doses) are used when agitation, paranoia, and hallucinations are present. Low dose benzodiazepines and trazodone are often used for anxiety, agitation, or insomnia.