Dementia: Definition and Natural History

Although there are many types of dementia, they have a number of features in common. This section contains a discussion of dementia in general and brief descriptions of some of its more common types.

A. Definition Of Dementia

The essential features of a dementia are multiple cognitive deficits that include memory impairment and at least one of the following: aphasia, apraxia, agnosia, or a disturbance in executive functioning (the ability to think abstractly and to plan, initiate, sequence, monitor, and stop complex behavior). The order of onset and relative prominence of the cognitive disturbances and associated symptoms vary with the specific type of dementia, as discussed in the following.

Memory impairment is generally a prominent early symptom. Individuals with dementia have difficulty learning new material and may lose valuables, such as wallets and keys, or forget food cooking on the stove. In more severe dementia, individuals also forget previously learned material, including the names of loved ones. Individuals with dementia may have difficulty with spatial tasks, such as navigating around the house or in the immediate neighborhood (where difficulties with memory are unlikely to play a role). Poor judgment and poor insight are common as well. Individuals may exhibit little or no awareness of memory loss or other cognitive abnormalities. They may make unrealistic assessments of their abilities and make plans that are not congruent with their deficits and prognosis (e.g., planning to start a new business). They may underestimate the risks involved in activities (e.g., driving).

In order to make a diagnosis of dementia, the cognitive deficits must be sufficiently severe to cause impairment in occupational or social functioning and must represent a decline from a previous level of functioning. The nature and degree of impairment are variable and often depend on the particular social setting of the individual. For example, mild cognitive impairment may significantly impair an individual's ability to perform a complex job but not a less demanding one.

B. Associated Features

Some individuals with dementia show disinhibited behavior, including making inappropriate jokes, neglecting personal hygiene, exhibiting undue familiarity with strangers, or disregarding conventional rules of social conduct. Occasionally, they may harm others by striking out. Suicidal behavior may occur, especially in mildly impaired individuals, who are more likely to have insight into their deficits and to be capable of formulating (and carrying out) a plan of action. Anxiety is fairly common, and some patients manifest "catastrophic reactions," overwhelming emotional responses to relatively minor stressors, such as changes in routine or environment. Depressed mood, with or without neurovegetative changes, is quite common, as are sleep disturbances independent of depression. Delusions can occur, especially those involving themes of persecution (e.g., the belief that misplaced possessions have been stolen). Misidentifications of familiar people as unfamiliar (or vice versa) frequently occur. Hallucinations can occur in all sensory modalities, but visual hallucinations are most common. Some patients exhibit a peak period of agitation (or other behavioral disturbances) during the evening hours, which is sometimes referred to as "sundowning."

Delirium is frequently superimposed on dementia because the underlying brain disease increases susceptibility to the effects of medications or concurrent general medical conditions. Individuals with dementia may also be especially vulnerable to psychosocial stressors (e.g., going to the hospital, bereavement), which may exacerbate their intellectual deficits and associated problems.

Dementia is sometimes accompanied by motor disturbances, which may include gait difficulties, slurred speech, and a variety of abnormal movements. Other neurological symptoms, such as myoclonus and seizures, may also occur.

C. Differential Diagnosis

The differential diagnosis of dementia is described in detail in DSM-IV (1) and is summarized only briefly here. Memory impairment occurs in both delirium and dementia. Delirium is also characterized by a reduced ability to maintain and shift attention appropriately, but the cognitive deficits tend to fluctuate, while those of dementia tend to be stable or progressive. An amnestic disorder is characterized by memory impairment without significant impairment in other cognitive domains. Mental retardation has an onset before age 18 and is characterized by significantly subaverage general intellectual functioning, which does not necessarily include memory impairment. Schizophrenia may be associated with multiple cognitive impairments and a decline in functioning, but the cognitive impairment tends to be less severe and occurs against a background of psychotic and behavioral symptoms meeting the established diagnostic criteria. Particularly in elderly persons, major depressive disorder may be associated with complaints of memory impairment, difficulty concentrating, and a reduction in intellectual abilities shown by history or mental status examination; this is sometimes referred to as pseudodementia.

The two may sometimes be distinguished on the basis of an assessment of the course and onset of depressive and cognitive symptoms and by response to treatment of the depression. However, even when the onset of depressive symptoms precedes or coincides with the onset of cognitive symptoms and both resolve with antidepressant treatment, as many as one-half of patients go on to develop an irreversible dementia within 3 years (2). Dementia must be distinguished from malingering and factitious disorder, which generally manifest patterns of cognitive deficits that are inconsistent over time and are uncharacteristic of those typically seen in dementia. Dementia must also be distinguished from age-related cognitive decline, the mild decline in cognitive functioning that may occur with aging, which is nonprogressive and does not lead to functional impairment.

D. Prevalence And Course

Exact estimates of the prevalence of dementia depend on the definition and specific threshold used, but it is clear that the prevalence increases dramatically with age. The syndrome affects approximately 5%-8% of individuals over age 65, 15%-20% of individuals over age 75, and 25%-50% of individuals over age 85. Alzheimer's disease is the most common dementia, accounting for 50%-75% of the total, with a greater proportion in the higher age ranges. Vascular dementia is probably next most common, but its prevalence is unknown. The remaining types of dementia account for a much smaller fraction of the total, although in the last few years it has been suggested that Lewy body disease may be more prevalent than previously realized (3).

The mode of onset and subsequent course of dementia depend on the underlying etiology. Classically, Alzheimer's disease has an insidious onset and gradual decline, while vascular dementia is characterized by a more acute onset and stepwise decline. However, since both disorders are common, the two frequently coexist, although only one diagnosis may be made during a person's life. Other dementias may be progressive, static, or remitting. The reversibility of a dementia is a function of the underlying pathology and of the availability and timely application of effective treatment.

E. Staging Of Dementia

Progressive dementias are generally staged according to the level of functional impairment, and the same categories may be used to describe the degree of severity of any dementia (4, 5). The ability to perform a specific function depends on baseline skills, deficits, and the social environment, so the severity of illness should be assessed in the context of past functioning in several domains. Individuals with questionable impairment show borderline functioning in several areas but definite impairment in none. Such individuals are not considered demented, but they should be evaluated over time: some may progress to a dementing disorder, some may return to normal functioning, and others may remain in a questionable state. Individuals with mild impairment are likely to have difficulties with balancing a checkbook, preparing a complex meal, or managing a difficult medication schedule. Those with moderate impairment also have difficulties with simpler food preparation, household cleanup, and yard work and may require assistance with some aspects of self-care (e.g., reminders to use the bathroom, help with fasteners or shaving). Those whose dementia is severe require considerable assistance with personal care, including feeding, grooming, and toileting. In profound dementia, the patients may become largely oblivious to their surroundings and are almost totally dependent on caregivers. In the terminal phase, patients are generally bed bound, require constant care, and may be susceptible to accidents and infectious diseases, which often prove fatal.

F. Specific Dementias

1. Dementia of the Alzheimer's type Dementia of the Alzheimer's type, referred to here for brevity as Alzheimer's disease, is a dementia with an insidious onset and gradual progression. Various patterns of deficits are seen, but the disorder begins most commonly with deficits in recent memory, which are followed by aphasia, apraxia, and agnosia after several years. Deficits in executive function (e.g., performing tasks involving multiple steps, such as balancing a checkbook or preparing a meal) are also typically seen early in the course of the disease. Some individuals may show personality changes or increased irritability in the early stages. In the middle and later stages of the disease, psychotic symptoms are common. Patients also tend to develop incontinence and gait and motor disturbances, and eventually they become mute and bedridden. Seizures and myoclonus may also occur late in the disease.

The diagnosis of Alzheimer's disease should be made only when other etiologies for the dementia have been ruled out by careful history, physical and neurological examinations, and laboratory tests. A definitive diagnosis of Alzheimer's disease depends on microscopic examination of the brain (generally at autopsy), which reveals numerous characteristic senile plaques and neurofibrillary tangles widely distributed in the cerebral cortex. A clinical diagnosis of Alzheimer's disease conforms to the pathological diagnosis 70%-90% of the time.

Onset generally occurs in late life, most commonly in the 60s, 70s, and 80s and beyond, but in rare instances the disorder appears in the 40s and 50s. The incidence of Alzheimer's disease also increases with age, and it is estimated at 0.5% per year from age 65 to 69, 1% per year from age 70 to 74, 2% per year from age 75 to 79, 3% per year from 80 to 84, and 8% per year from age 85 onward (6). Progression is gradual but steadily downward, with an average duration from onset of symptoms to death of 8-10 years. Plateaus may occur, but progression generally resumes after 1 to several years.

DSM-IV subdivides Alzheimer's disease into the following subtypes, indicating the predominant feature of the current clinical presentation: With Delirium, With Delusions, With Depressed Mood (including but not limited to presentations that meet symptom criteria for a Major Depressive Episode), and Uncomplicated. In addition, the specifier "With Behavioral Disturbance" can also be used to indicate the presence of clinically significant difficulties, such as wandering or combativeness. DSM-IV further divides Alzheimer's disease arbitrarily into early onset, which is used if the symptoms of cognitive decline begin at or before age 65, and late onset, if they begin after age 65.

2. Vascular (multi- infarct) dementia Vascular dementia is a dementia due to the effects of one or more strokes on cognitive function. Typically, it is characterized by an abrupt onset and stepwise course in the context of cerebrovascular disease documented by history, focal neurological signs and symptoms, and/or imaging studies. The pattern of cognitive deficits is often patchy, depending on which regions of the brain have been destroyed. Certain cognitive functions may be affected early, whereas others remain relatively unimpaired. Associated focal neurological signs and symptoms include extensor plantar response, pseudobulbar palsy, gait abnormalities, exaggeration of deep tendon reflexes, and weakness of an extremity. Structural imaging studies usually indicate multiple vascular lesions of the cerebral cortex and subcortical structures.

The onset of vascular dementia may occur any time in late life but becomes less common after age 75, while the incidence of Alzheimer's disease continues to rise. The relationship between Alzheimer's disease and vascular dementia is complex, in part because Alzheimer's disease and strokes are both common and frequently coexist (although generally only one diagnosis is recognized during a person's life), and because recent evidence suggests that small strokes may lead to increased clinical expression of Alzheimer's disease (7). The degree to which strokes alone are responsible for dementia is unclear. However, one study estimated that 8% of individuals over 60 who have a stroke develop dementia within the following year, compared to 1% of age-matched individuals without a history of stroke (8). Vascular dementia tends to progress in a stepwise fashion but can be static. Early treatment of hypertension and vascular disease may prevent further progression.

Like Alzheimer's disease, vascular dementia is subtyped in DSM-IV according to any prominent associated symptoms: With Delirium, With Delusions, With Depressed Mood, and Uncomplicated. The additional modifier "With Behavioral Disturbance" may also be used. No subtyping based on age of onset is used.

3. Dementia due to Parkinson's disease Parkinson's disease is a slowly progressive neurological condition characterized by tremor, rigidity, bradykinesia, and postural instability; its onset is typically in middle to late life. In 20% to 60% of the cases, it is accompanied by a dementia, which is particularly common late in the course. The dementia associated with Parkinson's disease has an insidious onset and slow progression and is characterized by cognitive and motoric slowing, executive dysfunction, and impairment in memory retrieval. Parkinson's disease is important to psychiatrists because of the high prevalence of associated depression and the frequent occurrence of psychotic symptoms during pharmacologic treatment of the primary motor deficit.

4. Dementia due to Lewy body disease Lewy body disease is a recently characterized disorder (9) that is clinically fairly similar to Alzheimer's disease but tends to have earlier and more prominent visual hallucinations and parkinsonian features and a somewhat more rapid evolution. Patients are notably sensitive to extrapyramidal effects of antipsychotic medications. Histopathologically, it is marked by the presence of Lewy inclusion bodies in the cerebral cortex. Recent studies suggest that Lewy body disease may account for many as 7%-26% of dementia cases, depending on the criteria used (3). The disorder is particularly likely to come to psychiatric attention because of the patients' prominent psychotic symptoms and sensitivity to antipsychotic medications.

5. Dementia due to Pick's disease and other frontal lobe dementias Pick's disease and other frontal lobe dementias are characterized in their early stages by changes in personality, executive dysfunction, deterioration of social skills, emotional blunting, behavioral disinhibition, and prominent language abnormalities. Difficulties with memory, apraxia, and other features of dementia usually follow later in the course. Prominent primitive reflexes (snout, suck, grasp) may be present. As the dementia progresses, it may be accompanied by either apathy or extreme agitation. Individuals may develop such severe problems with language, attention, or behavior that it may be difficult to assess the degree of cognitive impairment. The diagnosis is difficult to make clinically, and it is especially difficult to distinguish from atypical Alzheimer's disease. In Pick's disease, structural brain imaging typically reveals prominent frontal and/or temporal atrophy, with relative sparing of the parietal and occipital lobes. The diagnosis of Pick's disease must be confirmed by the autopsy finding of characteristic Pick inclusion bodies. Other frontal lobe dementias tend to have more nonspecific histopathology. The disorder most commonly manifests itself in individuals between the ages of 50 and 60 years, although it can occur among older individuals. The course is progressive and tends to be more rapid than that of Alzheimer's disease. These disorders are fairly rare but are important for psychiatrists because they often present with psychiatric symptoms.

6. Other progressive dementing disorders A number of other disorders can lead to progressive dementia. These include Huntington's disease-an autosomal dominant disorder that affects the basal ganglia and other subcortical structures and includes motor, behavioral, and cognitive symptoms-and Creutzfeldt-Jakob disease-a rapidly progressive spongiform encephalopathy associated with a slow virus or a prion (proteinaceous infectious particle).

7. Dementia due to other causes In addition to the preceding categories, a number of general medical conditions can cause dementia. These conditions include structural lesions (primary or secondary brain tumor, subdural hematoma, slowly progressive or normal-pressure hydrocephalus), head trauma, endocrine conditions (hypothyroidism, hypercalcemia, hypoglycemia), nutritional conditions (deficiency of thiamin, niacin, or vitamin B12), other infectious conditions (HIV, neurosyphilis, Cryptococcus), derangements of renal and hepatic function, neurological conditions (e.g., multiple sclerosis), effects of medications (e.g., benzodiazepines, ß blockers, diphenhydramine), and the toxiceffect of long-standing substance abuse, especially alcohol abuse. It is critical that psychiatrists caring for demented individuals be familiar with the general medical and neurological causes of dementia in order to assure that the diagnosis is accurate and, in particular, that potentially treatable conditions are not missed.

Excerpted from "The American Psychiatric Association's Practice Guideline for the Treatment of Patients With Alzheimer's Disease and Other Dementias of Late Life" This practice guideline was approved in December 1996 and was published in May 1997.

© Copyright 2000 American Psychiatric Association

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