Alzheimer's Disease

In Alzheimer's disease, the ability to remember, think, understand, communicate, and control behavior progressively declines because brain tissue degenerates.

Alzheimer's disease accounts for most dementias in older people. It is very rare among people under 60. Alzheimer's disease becomes more common as people age. It affects only about 1 to 3% of people aged 60 to 64 but up to 30% of those over 85. In the United States, about 4 million people have Alzheimer's disease.

In Alzheimer's disease, brain tissue degenerates in a particular way. Nerve cells are lost. Tangles (neurofibrillary tangles) form in nerve cells, and clumps (senile or amyloid plaques) form between nerve cells. People with Alzheimer's disease also have a low level of acetylcholine in the brain. Acetylcholine is a chemical that helps nerve cells communicate with one another.

See the figure Tangles and Plaques.

Some people with Alzheimer's disease also have atherosclerosis. Atherosclerosis can lead to strokes, which sometimes result in vascular dementia. Thus, such people may have two types of dementia (mixed dementia).

Causes

What causes degeneration of brain tissue in Alzheimer's disease is unknown. For most people, the cause seems to be a combination of genes and environment. But the environmental factors involved are not yet known. For some people, genes appear to be more important. The disease seems to run in some families, particularly when it develops at an early age.

For additional detail on this topic, see Apolipoprotein E and Alzheimer's Disease.

Symptoms

The symptoms of Alzheimer's disease are similar to those of other dementias. They include memory loss, changes in personality, problems using language, disorientation, difficulty doing daily activities, and disruptive behavior. A person with Alzheimer's disease may not have all the symptoms.

Symptoms usually begin subtly. People may not notice any changes at first, depending on what activities they are involved in. At some point, people with Alzheimer's disease may notice they are not doing their job or activities quite as well as in the past.

In most people with Alzheimer's disease, the first sign is forgetting recent events. But the disease may begin with changes in personality. For example, people may become emotionally unresponsive, depressed, or unusually fearful or anxious. Or emotions may rapidly and unpredictably change from one extreme to another. Early in the disease, people have difficulty using language. They may use a general word or many words rather than a specific word, use words incorrectly, or be unable to find the right word. They become less able to use good judgment and think abstractly.

Disruptive or inappropriate behavior is common. People with Alzheimer's disease may become agitated, irritable, hostile, and physically aggressive. Many of them wander.

Many people with Alzheimer's disease have insomnia. They have trouble falling or staying asleep. Some people become confused about day and night. Thinking it is day, they may get up and get dressed in the middle of the night.

As Alzheimer's disease progresses, some people have psychotic symptoms, such as hallucinations, delusions, or paranoia.

Progression is unpredictable. After symptoms begin, people live, on average, 8 to 10 years. During a good part of this time, many people continue to enjoy much of what they enjoyed before developing Alzheimer's disease. But eventually, as in all dementias, memory is completely lost, and people with Alzheimer's disease become totally dependent on others. Once people can no longer walk, they live, on average, about 6 months. However, there is considerable variation, and some bed-bound people live for several years.

Diagnosis

If dementia is diagnosed in an older person and the person's memory has gradually deteriorated, doctors suspect Alzheimer's disease. The diagnosis is based partly on symptoms, which are identified by asking the person and family members or other caregivers questions. The diagnosis is also based on a physical examination and the results of tests, such as mental status tests, blood and urine tests, and computed tomography (CT) or magnetic resonance imaging (MRI). This information helps doctors exclude other types and causes of dementia. Such a diagnosis is correct most of the time.

The diagnosis of Alzheimer's disease can be confirmed only when a sample of brain tissue is removed (rarely done until after death) and examined under a microscope. Then, the characteristic loss of nerve cells, neurofibrillary tangles, and senile plaques can be seen throughout the brain. Positron emission tomography (PET) and analysis of spinal fluid have been suggested as ways to diagnose Alzheimer's disease. However, these tests are not yet accurate enough for widespread use.

Treatment

Generally, treatment of Alzheimer's disease is the same as that of all dementias. Cholinesterase inhibitors may stabilize or slightly improve mental function (including memory). But they cannot stop the progression of Alzheimer's disease. Ginkgo biloba is sometimes used. Evidence of its effectiveness is inconclusive.

Researchers continue to study drugs that may prevent or slow the progression of Alzheimer's disease. Nonsteroidal anti-inflammatory drugs (NSAIDs), commonly used to treat arthritis, are an example. Vitamin E may also help prevent and slow progression of the disease, although study results are unclear. Before any of these substances are taken, their risks and benefits should be discussed with a doctor.

If people with Alzheimer's disease also have atherosclerosis, conditions that make atherosclerosis worse (and thus stroke more likely) are corrected or eliminated.