What are dementias?

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A group of disorders involving pervasive, progressive, and irreversible decline in cognitive functioning resulting from a variety of causes.
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Causes and Symptoms

Dementia affects an estimated 35.6 million people worldwide, according to the World Health Organization (WHO) in 2012, with approximately 7.7 million new cases diagnosed each year. It is a major cause of disability in individuals over sixty, with a prevalence that increases with age. Dementia is characterized by a permanent memory deficit affecting recent memory in particular, of sufficient severity to interfere with the patient’s ability to take part in professional and social activities.

Dementia is not part of the normal aging process. It also is not synonymous with benign senescent forgetfulness, which is more common and also affects recent memory. Although the latter is a source of frustration, it does not significantly interfere with the individual’s professional and social activities because it tends to affect only trivial matters (or what the individual considers trivial). Furthermore, patients with benign forgetfulness usually can remember what was forgotten by using a number of strategies, such as writing lists or notes to themselves and leaving them in conspicuous places. Individuals with benign forgetfulness also are acutely aware of their memory deficit, while those with dementia, except in the early stages of the disease or in certain types of dementia, generally have no insight into their memory deficit and often blame others for their problems.

In addition to the memory deficit, patients with dementia often show evidence of impaired abstract thinking, impaired judgment, or other disturbances of higher cortical functions, such as aphasia (the inability to use or comprehend language), apraxia (the inability to execute complex, coordinated movements), or agnosia (the inability to recognize familiar objects).

Dementia may result from damage to the cerebral cortex (the outer layer of the brain), as in Alzheimer’s disease, or from damage to the subcortical structures (the structures below the cortex), such as white matter, the thalamus, or the basal ganglia. Although memory is impaired in both cortical and subcortical dementias, the associated features are different. In cortical dementias, for example, cognitive functions such as the ability to talk and understand speech and the ability to perform mathematical calculations are severely impaired. In subcortical dementias, there is evidence of disturbances of arousal, motivation, and mood in addition to a significant slowing of cognition and of information processing.

Alzheimer’s disease, the most common cause of presenile dementia, is characterized by progressive disorientation, memory loss, speech disturbances, and personality disorders. Pick’s disease is another cortical dementia, but unlike Alzheimer’s disease, it is rare, tends to affect younger patients, and is more common in women. In the early stages of Pick’s disease, changes in personality, absence of inhibition, inappropriate social and sexual conduct, and lack of foresight may be evident—features that are not common in Alzheimer’s disease. Patients also may become euphoric or apathetic. Poverty of speech is often present and gradually progresses to mutism, although speech comprehension is usually spared. Pick’s disease is characterized by cortical atrophy localized to the frontal and temporal lobes.

Vascular dementia is another common cause of dementia in patients over the age of sixty-five and is solely responsible for an estimated 10 percent of all dementia cases, according to the Alzheimer's Association, though it may be a contributing factor in as many as 30 percent of cases. It is caused by interference with the blood flow to the brain. Although the overall prevalence of vascular dementia is decreasing, there are some geographical variations, with the prevalence being higher in countries with a high incidence of cardiovascular and cerebrovascular diseases, such as Finland and Japan. Some patients with dementia have both Alzheimer’s disease and vascular dementia. Several types of vascular dementia have been identified.

Multi-infarct dementia (MID) is the most common type of vascular dementia. As its name implies, it is the result of multiple, discrete cerebral infarcts (strokes) that have destroyed enough brain tissue to interfere with the patient’s higher mental functions. The onset of MID is usually sudden and is associated with neurological deficits, such as the paralysis or weakness of an arm or leg or the inability to speak. The disease characteristically progresses in steps: with each stroke experienced, the patient’s condition suddenly deteriorates and then stabilizes or even improves slightly until another stroke occurs. In some cases, however, the disease displays an insidious onset and causes gradual deterioration. Most patients also show evidence of arteriosclerosis and other factors predisposing them to the development of strokes, such as hypertension, cigarette smoking, high blood cholesterol, diabetes mellitus, narrowing of one or both carotid arteries, or cardiac disorders, especially atrial fibrillation (an irregular heartbeat). Somatic complaints, mood changes, depression, and nocturnal confusion tend to be more common in vascular dementias, although there is relative preservation of the patient’s personality. In such cases, magnetic resonance imaging (MRI) or a computed tomography (CT) scan of the brain often shows evidence of multiple strokes.

Strokes are not always associated with clinical evidence of neurological deficits, since the stroke may affect a “silent” area of the brain or may be so small that its immediate impact is not noticeable. Nevertheless, when several of these small strokes have occurred, the resulting loss of brain tissue may interfere with the patient’s cognitive functions. This is the basis of the lacunar dementias: the infarcted tissue is absorbed into the rest of the brain, leaving a small cavity or lacuna. Brain-imaging techniques and especially MRI are useful in detecting these lacunae.

A number of neurological disorders are associated with dementia. The combination of dementia, urinary incontinence, and muscle rigidity causing difficulties in walking should raise the suspicion of hydrocephalus. In this condition, fluid accumulates inside the ventricles (cavities within the brain) and results in increased pressure on the brain cells. A CT scan demonstrates enlargement of the ventricles. Although some patients may respond well to surgical shunting of the cerebrospinal fluid, it is often difficult to identify those who will benefit from surgery. Potential postoperative complications are significant and include strokes and subdural hematomas.

Dementia has been linked to Parkinson’s disease, a chronic, progressive neurological disorder that usually manifests itself in middle or late life. It has an insidious onset and a very slow progression rate. Although intellectual deterioration is not one of the classical features of Parkinson’s disease, dementia is being recognized as a late manifestation of the disease, with as many as 50 to 80 percent of patients eventually being afflicted, according to the Alzheimer's Association. The dementing process also has an insidious onset and slow progression rate. Some of the medication used to treat Parkinson’s disease also may induce confusion, particularly in older patients.

Subdural hematomas (collections of blood inside the brain) may lead to mental impairment and are usually precipitated by trauma to the head. Usually, the trauma is slight and the patient neither loses consciousness nor experiences any immediate significant effects. A few days or even weeks later, however, the patient may develop evidence of mental impairment. By this time, the patient and caregivers may have forgotten about the slight trauma that the patient experienced. A subdural hematoma should be suspected in the presence of a fairly sudden onset and progressing course. Headaches are common. A CT scan can reveal the presence of a hematoma. The surgical removal of the hematoma is usually associated with a good prognosis if performed in a timely manner, before irreversible brain damage occurs.

Brain tumors may lead to dementia, particularly if they are slow growing. Most tumors of this type can be diagnosed by CT scanning or MRI. Occasionally, cancer may induce dementia through an inflammation of the brain.

Many chronic infections affecting the brain can lead to dementia. These include conditions that, when treated, may reverse or prevent the progression of dementia, such as syphilis, tuberculosis, slow viruses, and some fungal and protozoal infections. Human immunodeficiency virus (HIV) infection is also a cause of dementia, and it may be suspected if the rate of progress is rapid and the patient has risk factors for the development of HIV. Although dementia is part of the acquired immunodeficiency syndrome (AIDS) complex, it may occasionally be the first manifestation of the disease.

It is often difficult to differentiate depression from dementia. Nevertheless, sudden onset—especially if preceded by an emotional event, the presence of sleep disturbances, and a history of previous psychiatric illness—is suggestive of depression. The level of mental functioning of patients with depression is often inconsistent. They may, for example, be able to give clear accounts of topics that are of personal interest to them but be very vague about, and at times not even attempt to answer, questions on topics that are of no interest to them. Variability in performance during testing is suggestive of depression, especially if it improves with positive reinforcement.

Treatment and Therapy

It is estimated that in the United States, dementia affects about 1.1 percent of the population aged sixty to sixty-four years, as reported by WHO in 2012. (Estimated percentages vary throughout the rest of the world, ranging from 0.3 percent in west sub-Saharan Africa to 1.6 percent in Southeast Asia and western Europe.) By age eighty-five and higher, however, it affects anywhere from 21.7 to 47.5 percent of Americans. While different surveys may yield different results, depending on the criteria used to define dementia, it is clear that this is a significant problem.

For physicians, an important aspect of diagnosing patients with dementia is detecting potentially reversible causes that may be responsible for the impaired mental functions. A detailed history, a meticulous and thorough clinical examination, and a few selected laboratory tests are usually sufficient to reach a diagnosis. Various investigators have estimated that reversible causes of dementia can be identified in 9 percent to 23 percent of patients. Recommended investigations include brain imaging (CT scanning or MRI), a complete blood count, and tests of erythrocyte sedimentation rate, blood glucose, serum electrolytes, serum calcium, liver function, thyroid function, and serum B12 and folate. Some investigators also recommend routine testing for syphilis. Other tests, such as HIV testing, cerebrospinal fluid examination, neuropsychological testing, drug and toxin screening, serum copper and ceruloplasmin analysis, carotid and cerebral angiography, and electroencephalography, are performed when appropriate.

It is of paramount importance for health care providers to adopt a positive attitude when managing patients with dementia. Although at present little can be done to treat and reverse dementia, it is important to identify its cause. In some cases, it may be possible to prevent the disease from progressing. For example, if the dementia is the result of hypertension, adequate control of this condition may prevent further brain damage. Moreover, the prevalence of vascular dementia is decreasing in countries where efforts to reduce cardiovascular and cerebrovascular diseases have been successful. Similarly, if the dementia is the result of repeated embolisms (blood clots reaching the brain) complicating atrial fibrillation, then anticoagulants or aspirin may be recommended.

Even after a diagnosis of dementia is made, it is important for the physician to be alert for other conditions that may worsen the patient’s mental functions, such as the inadvertent intake of medications that may induce confusion and mental impairment. Medications with this potential are numerous and include not only those that act on the brain, such as sedatives and hypnotics, but also hypotensive agents (especially if given in large doses), diuretics, and antibiotics. Whenever the condition of a patient with dementia deteriorates, the physician meticulously reviews all the medications that the patient is taking, both prescriptions and over-the-counter medications. Even if innocuous, some over-the-counter preparations may interact with other medications that the patient is taking and lead to a worsening of mental functions. Inquiries are also made into the patient’s alcohol intake. The brain of an older person is much more sensitive to the effects of alcohol than that of a younger person, and some medications may interact with the alcohol to further impair the patient’s cognitive functions.

Many other disease states also may worsen the patient’s mental functions. For example, patients with diabetes mellitus are susceptible to developing a variety of metabolic abnormalities, including a low or high blood glucose level, both of which may be associated with confusional states. Similarly, dehydration and acid-base or electrolyte disorders, which may result from prolonged vomiting or diarrhea, may also precipitate confusional states. Infections, particularly respiratory and urinary tract infections, often worsen the patient’s cognitive deficit. Finally, patients with dementia may experience myocardial infarctions (heart attacks) that are not associated with any chest pain but that may manifest themselves with confusion.

The casual observer of the dementing process is often overwhelmed with concern for the patient, but the process is often more difficult for the patient's family. Dementia patients themselves experience no physical pain or distress, and except in the very early stages of the disease, they are oblivious to their plight as a result of their loss of insight. Health care professionals therefore are alert to the stress imposed on the caregivers by dealing with loved ones with dementia. Adequate support from agencies available in the community is essential.

When a diagnosis of dementia is made, the physician discusses a number of ethical, financial, and legal issues with the family, as well as with the patient if it is believed that he or she can understand the implications of the discussion. Families are encouraged to make a list of all the patient’s assets, including insurance policies, and discuss this information with an attorney to protect the patient’s and the family’s assets. If the patient is still competent, it is recommended that he or she select a trusted person to have durable power of attorney. Unlike the regular power of attorney, the former does not become invalidated when the patient becomes mentally incompetent and remains in effect regardless of the degree of mental impairment of the person who executed it. Because durable power of attorney cannot be easily reversed once the person is incompetent, great care should be taken when selecting a person, and the specific powers granted should be clearly specified. It is also important for the patient to make his or her desires known concerning advance directives and the use of life-support systems.

Courts may appoint a guardian or conservator to have charge and custody of the patient’s property, including real estate and money, when no responsible family members or friends are willing or available to serve as guardian. Courts supervise the actions of the guardian, who is expected to report all the patient’s income and expenditures to the court once a year. The court may also charge the guardian to ensure that the patient is adequately housed, fed, and clothed and receiving appropriate medical care.

Perspective and Prospects

Dementia is a very serious and common condition, especially among the older population. Dementia permanently robs patients of their minds and prevents them from functioning adequately in their environment by impairing memory and interfering with the ability to make rational decisions. It therefore deprives patients of their dignity and independence.

Because dementia is mostly irreversible, cannot be adequately treated at present, and is associated with a fairly long survival period, it has a significant impact not only on the patient but also on the patient’s family and caregivers and on society in general. The expense of long-term care for patients with dementia, whether at home or in institutions, is staggering. Every effort, therefore, is made to reach an accurate diagnosis and especially to detect any other condition that may worsen the patient’s underlying dementia. Finally, health care professionals do not treat the patient in isolation but also concern themselves with the impact of the illness on the patient’s caregivers and family.

Much progress has been made in defining dementia and determining its cause. Terms such as senile dementia are no longer in use, and even the use of the term dementia to diagnose a patient’s condition is frowned upon because there are so many types of dementia. Identification of the type of dementia affecting a particular patient is important because of its practical implications, both for the patient and for research into the prevention, management, and treatment of dementia.

There is little that can be done to cure dementia and no effective means to regenerate nerve cells. Researchers, however, are feverishly trying to identify factors that control the growth and regeneration of nerve cells. Although no single medication is expected to be of benefit to all types of dementia, it is hoped that effective therapy for many dementias will be developed. In 2012, WHO announced that the number of people living with dementia would likely double by 2030 and triple by 2050, further underlining the need to develop improved treatments and methods for diagnosing dementia's many causes.


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