dementia in a nutshell

Dementia is a deterioration of the mental condition. Dementia usually occurs in old age, although rarer cases of presenile dementia are diagnosed. Terms used exclusively with dementia are chronic brain syndrome, organic mental syndrome, and senile confusional state.

The incidence of dementia is less than 10% of people over the age of 65, but perhaps a quarter of people over the age of 80 and half of all nursing home patients. Dementia is not the most common mental disorder in old age (ie, depression), nor should it be considered an inevitable concomitant of aging. Many people can preserve cognitive functioning well into their ninth decade.

The onset of most cases of dementia tends to be gradual. The first mental changes may be increased rigidity, suspiciousness, irritability, or depression. As the disorder progresses, deficits in short-term memory become pronounced. Patients can remember in great detail what happened years ago, but they cannot remember the answers to a question given five minutes ago. A woman in a nursing home could remember how to play a song she had learned in a Prohibition-era honky tonk, but when the other residents clapped and asked for another song, she played it again. The ability to follow instructions is also diminished, to the dismay of the patient’s caregivers. Disorientation in time develops: the patient does not know what day of the week it is. Next comes disorientation on the spot: the patient can get lost, even in familiar territory. The patient may develop aphasias, apraxias, perseverance and/or social withdrawal. In later stages, recognition of significant others may be lost, along with bowel and bladder functions. Death usually occurs when the patient loses the ability to swallow.

Dementia is different in type, rather than degree, from the forgetfulness that most elderly people complain of. Benign senescent forgetfulness is an age-associated memory impairment that does not have a serious prognostic implication. Nor is dementia analogous to a second childhood. Childhood play arises from a lack of knowledge about proper adult roles, while the demented elderly may manifest such behavior due to memory problems, confusion, or sensory/motor limitations. Some nursing home patients may act more like children if the staff rewards such behavior with attention, especially affection.

More than 50 different diseases can cause dementia. Huntington’s chorea is due entirely to the presence of a single dominant gene. Creutzfeld-Jakob disease is caused by a viral infection, perhaps due to the consumption of insufficiently cooked bovine brain. Kuru, a viral infection in Melanesia, can be spread through ritual cannibalism. Hydrocephalus is excessive pressure of the cerebrospinal fluid in the ventricles, which alters the functioning of the cortex. Chronic alcohol abuse, tertiary syphilis (general paresis), AIDS, encephalitis, subdural hematoma, Parkinson’s disease, intracranial neoplasia, head trauma, and meningitis are other possible causes.

The majority of demented geriatric patients suffer from Alzheimer’s disease (also known as senile dementia of the Alzheimer type), which results in specific degenerative diseases in brain tissues. A similar but rarer disorder is Pick’s disease, which usually affects people in their 50s and is primarily localized to the frontal and temporal lobes. These changes can be observed postmortem or by computed tomography.

Before 1980 it was assumed that the main cause of dementia was cerebral atherosclerosis, a hardening of the brain’s arteries that causes less oxygen to be delivered to brain tissues. The current consensus is that decreased blood flow is an important causal factor in only a minority of cases of dementia in old age. Oxygen depletion may be more a symptom of reduced cortical functioning than its cause. A major cause of dementia posed by the vascular system may be multi-infarct dementia: many small strokes that have the combined impact of diminishing cognitive ability without causing the paralysis characteristic of larger strokes.

The diagnosis of dementia cannot be based solely on the patient’s complaints about forgetfulness. There is no correlation between self-reported memory capacity and memory capacity as indicated by objective tests. Many of the elderly who complain most about memory decline are within the normal range but suffer from depression. Some completely insane patients do not perceive any difficulty with their memories.

The first step should be brief psychological screening tests. The use of Bender-Gestalt test scales, Intelligence Quotient, or other tests designed for other purposes or for other age groups should be avoided. Questions that test orientation in space and time are useful. The ability to draw a clock face with the hands and the dial is helpful. Focusing the test on short-term memory tends to neutralize some of the confounding variables and gives a truer indication of dementia. Many of these tests (eg, the Mental Status Questionnaire or the Folstein Mini-Mental Status Examination) have higher sensitivity than specificity: some normal elderly are more likely to be misdiagnosed with dementia than senile ones to get a score in the normal range. Whenever these screening tests suggest the presence of dementia, a complete neurological exam is appropriate.

One diagnostic difficulty is distinguishing organically based dementia from pseudodementia due to depression. Dementia is generally characterized by a gradual onset, while depression can have rapid progression of symptoms from environmental stress or loss. Depressed patients are more likely to complain of memory loss and give “I don’t know” responses. Patients with pure dementia are more likely to try to hide cognitive deficits or give ridiculous answers rather than admit they don’t know the answer. A complication for the differential diagnosis of depression is that self-report scales (eg, the Geriatric Depression Scale) may lose their validity as senile confusion increases: the patient may be unable to understand the questions. Another problem with the differential diagnosis is that the two disorders are not mutually exclusive. Awareness of cognitive decline can produce a depressive reaction, and a sizeable minority of patients with early-stage dementia develop clinically significant depression.

Another possibility is that the cognitive deficits are the result of a delirium or amnestic disorder rather than dementia. This may be the case for many confused elderly people admitted to general hospitals. What is needed is a knowledge of the details about the beginning, the course and the laboratory tests. Complicating factors are that patients with delirium cannot perform memory tests, and these disorders are not mutually exclusive.

Even with CT scans and lumbar punctures, the diagnosis of dementia is far from exact. Some patients are falsely labeled as insane, while other cases may go unnoticed until autopsy.

Treatment of dementia can be both medical and psychosocial. About a fifth of patients with dementia have a treatable organic cause (eg, hydrocephalus, which can be treated with surgery). The use of drugs has been much debated. While some patients report some benefit from tacrine or hydergine, some report side effects from the former and most report little benefit from the latter. Another controversial issue is the use of psychiatric medications (eg, antidepressants, antipsychotics) with patients with dementia. In many nursing homes, antidepressants are probably underused, while antipsychotics are often given to decrease behaviors that staff may find objectionable or inconvenient.

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