People fear dementia more than cancer, according to a poll from the United Kingdom reported in 2011. That shouldn't be surprising. In the past 25 years, cancer treatments have only gotten better, while treatments for dementia are discouragingly ineffective. And dementia as an illness may do more to destroy a person's sense of well-being.
The word dementia comes from the Latin words de ("out of") and mens ("the mind"). But it's now defined as a brain disorder that includes:
- Memory loss
- Deficits in cognition (thinking, planning and organizing abilities)
- A decline in emotional control or motivation
- Changes in behavior (such as increased irritability, apathy or problems interacting with other people).
It is difficult, if not impossible, to make a certain dementia diagnosis while a person is alive. Tests or brain images are of little practical help for making a diagnosis. The different types of dementia are defined based on problems that can only be seen by examining a person's brain after he or she has died.
Doctors make a dementia diagnosis based on the types of symptoms the person develops and how the illness progresses.
Here is a brief review of the most common dementia syndromes.
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Alzheimer's disease (also referred to as dementia of the Alzheimer's type) affects roughly 5 million Americans and more than 35 million people around the world. It is by far the most common dementia. About 50% to 56% of people with dementia are diagnosed with Alzheimer's. Another 13% to 17% also have the related disorder vascular dementia.
The diagnosis of Alzheimer's is based on finding specific abnormalities in and around nerve cells. These are called "beta-amyloid plaques" and "neurofibrillary tangles." They may be present in any aging brain, but people with Alzheimer's have more of these defects.
Alzheimer's disease affects areas of the brain involved in learning and memory. Therefore a common symptom is difficulty in recalling new information. Memory loss disrupts daily life. The person may get lost in a previously familiar neighborhood. He or she may also have difficulty making decisions, solving problems or making good judgments. Mood and personality may change. A person might become more irritable, hostile or apathetic.
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The second most common type of dementia is vascular dementia. The term, "vascular," refers to blood vessels — in this case, the blood vessels that feed the brain. The loss of brain tissue in vascular dementia results from blockages in that blood supply. This deprives brain cells of oxygen, causing them to die.
When a significant part of the brain is deprived of oxygen, a stroke occurs. But in vascular dementia, a person loses small batches of cells at a time. In effect, multiple small strokes occur.
This process creates a "stepwise" pattern of decline. (In contrast, Alzheimer's decline is gradual.) But the steps may be so small that the changes appear gradual.
Symptoms in vascular dementia depend on the area and extent of brain damage. Thus, the cardinal feature of Alzheimer's — memory loss — may or may not occur with vascular dementia. Likewise, specific thinking deficits may appear (such as difficulties calculating), while other mental abilities (such as planning) may remain intact.
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A person with mixed dementia has the Alzheimer's type plus another type of dementia, most often vascular dementia. The fact that these often co-occur makes sense, given that atherosclerosis and vascular disease contribute to the development of both types of dementia. (Atherosclerosis is an illness where substances, such as fat and cholesterol, build up inside blood vessels. This causes them to stiffen and reduces blood flow.)
Unfortunately, when a person has both of these dementias, the brain damage and resulting mental deterioration may be particularly severe.
A person's symptoms may be more typical of Alzheimer's or of the co-occurring dementia. Mixed dementia is most likely in a patient with cardiovascular disease, such as someone with high cholesterol levels, high blood pressure or evidence of atherosclerosis, who also develops dementia.
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Lewy Body Dementia
Lewy bodies are named for the scientist who discovered them. They are abnormal deposits in brain cells of a protein called alpha-synuclein. This protein's function is not well understood, but it may have a role in communication between nerve cells.
These lesions are also found in some patients with Alzheimer's and in those with Parkinson's disease, but they are the hallmark of Lewy body dementia.
As with most dementias, this diagnosis can only be made by examining the brain after death. Clinicians diagnose the condition on the basis of symptoms, such as visual hallucinations, fluctuating levels of alertness during the day and movement disorders reminiscent of Parkinson's (such as stiffness, shuffling gait, balance problems that cause falls, and lack of facial expression).
About half of the people affected also have a rapid-eye-movement (REM) sleep disorder in which they thrash about while dreaming or act out their dreams. (During normal REM sleep, physical movement is suppressed.) In addition, patients with Lewy body dementia may have symptoms similar to those of Alzheimer's, such as memory problems, confusion and other mental impairments.
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Frontotemporal dementia develops when brain damage occurs in the front (frontal lobes) and sides (the temporal lobes) of the brain. The source of the brain damage remains unclear, although autopsies have revealed abnormalities known as Pick bodies (a subtype of this dementia known as Pick's disease). In most cases of this type of dementia, the frontal and temporal lobes shrink as the disease progresses.
With this type of dementia, symptoms tend to appear more suddenly than in Alzheimer's or some other dementias. The disease then gets worse steadily. Usually it first causes changes in personality and behavior. A previously polite person may start making rude remarks, for example. Or a conservative spender may suddenly splurge on a questionable purchase.
The disorder may cause apathy and impair judgment or the ability to gauge other people's reactions. People often have fewer problems with their memory and they continue to be aware of their surroundings.
Many Types, Few Treatments
Unfortunately, recognizing the differences between types of dementia may not be much solace. That's because once a dementia has developed, it is usually hard to reverse. In a small number of cases, a doctor may be able to find a treatable cause for mental decline. Dietary deficiencies, medications, infections, alcohol use and depression can all cause symptoms of dementia. All of these illnesses can be treated.
The best approach to dementia is to do whatever you can to ward it off. Lifestyle changes that reduce your risk of cardiovascular disease, for example, can diminish the chances of developing dementia. Healthy living, as it turns out, is as good for your brain as it is for the rest of your body.
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Michael Craig Miller, M.D. is the former editor-in-chief of the Harvard Mental Health Letter and an assistant professor of psychiatry at Harvard Medical School. Dr. Miller has an active clinical practice and has been on staff at Beth Israel Deaconess Medical Center for more than 30 years.