While each patient is an individual case, mild to moderate Alzheimer's usually lasts two to 10 years, while advanced Alzheimer's can persist for up to five years [source: Alzheimer's Association]. The symptoms of Alzheimer's disease often aren't noticeable when they begin. Occasional lapses of memory are seen as common behavior for seniors and don't necessarily mean that someone is sick, though it is one of Alzheimer's early symptoms. Experts also point out that while forgetting unfamiliar people is not unusual, it isn't normal to forget those who one interacts with regularly.
As the disease progresses, severe forgetfulness sets in. A person will forget how to do things, even those that have been part of a daily routine for years. He or she will have difficulty remembering who people are. Thinking becomes muddled. The patient may have trouble assessing and judging situations or following directions. So-called "abstract thinking," such as manipulating information or numbers in one's head, is a particular problem. There can also be problems with spatial sense -- determining the locations of people and things relative to one's self.
At first a patient may have trouble remembering a word or phrase, but eventually, basic communication skills become impaired. Reading, writing and speaking all prove difficult. In moderate to advanced stages of Alzheimer's disease, a person can become confused, have mood swings, appear restless and wander off. Even a patient's personality may change, characterized by depression, restless or aggressive behavior, and anxiety.
Near end stage, an Alzheimer's patient must receive constant monitoring and care. By this point, neurons have died throughout the brain. The brain has shrunk, particularly in the cortex and hippocampus.
With Alzheimer's, there are many related diseases and complications, some of which can be fatal. Falls or accidents caused by loss of balance, disorientation or wandering off are common. These incidents may cause death on their own or may lead to other potentially deadly complications -- surgery, infections such as pneumonia, blood clots. In fact, while Alzheimer's disease is 100 percent fatal, the most common cause of death for those with the disease is some other acquired infection [source: NINDS]. But some states still list Alzheimer's disease as the cause of death in these cases, however. It's important to note that a patient can die from Alzheimer's itself: For example, the brain can become so damaged that a sufferer may no longer "know" how to breathe or may choke on food.
On the next page, we'll take a look at how a doctor diagnoses Alzheimer's disease.