Alzheimer's disease is a condition in which nerve cells in the brain die, making it difficult for the brain's signals to be transmitted properly. A person with Alzheimer's disease has problems with memory, judgment, and thinking, which makes it hard for the person to work or take part in day-to-day life. The death of the nerve cells occurs gradually over a period of years.

Once thought to be rare, Alzheimer's disease is the leading cause of dementia.

What Are the Symptoms of Alzheimer's Disease?

Most patients' symptoms progress slowly over a number of years. Symptoms may not be noticed early on. Sometimes, it is only when family members look back that they realize when the changes started to occur.

Common symptoms of Alzheimer's disease include:

• Impaired memory and thinking. The person has difficulty remembering things or learning new information. In the later stages of the disease, long-term memory loss occurs, which means that the person can't remember personal information, such as his or her place of birth or occupation, or names of close family members.
• Disorientation and confusion. People with Alzheimer's disease may get lost when out on their own and may not be able to remember where they are or how they got there. They may not recognize previously familiar places and situations. They also may not recognize familiar faces or know what time of the day it is, or even what year it is.
• Misplacing things. The person forgets where he or she put things used every day, such as glasses, a hearing aid, keys, etc. The person may also put things in strange places, such as leaving their glasses in the refrigerator.
• Abstract thinking. People with Alzheimer's disease may find certain tasks -- such as balancing a checkbook -- more difficult than usual. For example, they might forget what the numbers mean and what needs to be done with them.
• Trouble performing familiar tasks. The person begins to have difficulty performing daily tasks, such as eating, dressing, and grooming. Planning for normal day-to-day tasks is also impaired.
• Changes in personality and behavior. The person becomes unusually angry, irritable, restless, or quiet. At times, people with Alzheimer's disease can become confused, paranoid, or fearful.
• Poor or decreased judgment. People with Alzheimer's disease may leave the house on a cold day without a coat or shoes, or could go to the store wearing their pajamas.
• Inability to follow directions. The person has difficulty understanding simple commands or directions. The person may get lost easily and begin to wander.
• Problems with language and communication. The person can't recall words, name objects (even ones that are very familiar to them -- like a pen), or understand the meaning of common words.
• Impaired visual and spatial skills. The person loses spatial abilities (the ability to judge shapes and sizes, and the relationship of objects in space) and can't arrange items in a certain order or recognize shapes.
• Loss of motivation or initiative. The person may become very passive and require prompting to become involved and interact with others.
• Loss of normal sleep patterns. The person may sleep during the day and be wide-awake at night.

How Is It Diagnosed?

It is important to visit a doctor if you or a loved one experiences any of these symptoms so you can receive the proper evaluation and diagnosis. There are other conditions -- such as depression, a head injury, certain chemical imbalances, or the effects of some medications --that can produce symptoms that are similar to Alzheimer's disease. Many of these conditions are treatable.

Your doctor can only determine if the symptoms are probably due to Alzheimer's disease after a thorough medical, psychiatric, and neurological evaluation. He will evaluate other possible causes of dementia to rule out all other factors before settling on Alzheimer's disease as a diagnosis.

Currently, no definitive diagnostic test for Alzheimer's exists. A definite diagnosis of Alzheimer's disease is possible only after death, when a pathologist can more closely examine a patient's brain for the telltale changes associated with Alzheimer's disease.

What's the Prognosis?

The course of Alzheimer's disease varies widely from person to person. The duration of the illness could be short (2-3 years) or long (up to 20 years). Usually the parts of the brain that control memory and thinking are affected first, but over time, cells die in other areas of the brain.

Eventually, a person with Alzheimer's will need complete care. If the person has no other serious illnesses, the loss of brain function itself will eventually cause death.

Can Alzheimer's Disease be Prevented?

Because the exact cause of Alzheimer's disease is not known, there is currently nothing that can be done to guarantee its prevention. Some interventions may be worth incorporating into your life as more research reveals some potentially controllable risk factors. Staying mentally and physically active, maintaining a normal blood pressure and avoiding head injury by wearing seat belts and helmets may decrease your chances of developing Alzheimer's dementia.

It is important to remember, however, that there are causes of dementia other than Alzheimer's disease that may be preventable such as eating properly, exercising, quitting smoking, and limiting how much alcohol you drink. Your doctor can advise you about other healthy lifestyle habits you can adopt that may help prevent dementia.

Doctors have categorized Alzheimer's into the following types:

• Early onset Alzheimer's. This is a rare form of Alzheimer's disease in which people are diagnosed with the disease before age 65. Less than 10% of all Alzheimer's disease patients have this type. Because they experience premature aging, people with Down syndrome are particularly at risk for a form of early onset Alzheimer's disease. Adults with Down syndrome are often in their mid- to late 40s or early 50s when symptoms first appear.

  Younger people who develop Alzheimer's disease have more of the brain abnormalities that are associated with Alzheimer's disease. Early onset Alzheimer's appears to be linked with a genetic defect on chromosome 14, to which late-onset Alzheimer's is not linked. A condition called myoclonus -- muscle twitching and spasm -- also is more commonly seen in early onset Alzheimer's than in late-onset Alzheimer's.
   

• Late-onset Alzheimer's. This is the most common form of Alzheimer's disease, accounting for about 90% of cases and usually occurring after age 65. Late-onset Alzheimer's disease strikes almost half of all people over the age of 85 and may or may not be hereditary. Late-onset dementia is also called sporadic Alzheimer's disease.
   
• Familial Alzheimer's disease (FAD). This is a form of Alzheimer's disease that is known to be entirely inherited. In affected families, members of at least two generations have had Alzheimer's disease. FAD is extremely rare, accounting for less than 1% of all cases of Alzheimer's disease. It has a much earlier onset (often in the 40s) and can be clearly seen to run in families.