Alzheimer's disease (Alzheimer disease) is one of many causes of dementia, an impairment in memory and thinking that is severe enough to affect an individual's ability to function in daily life. Symptoms of Alzheimer's disease are subtle at first and may be identical to those associated with other causes of dementia. While this article is a guide to the symptoms associated with various stages of Alzheimer's disease, the diagnosis of the condition must be made by a doctor who can determine the exact cause of the symptoms and rule out other causes of dementia. Alzheimer's disease begins with a mild, slowly worsening memory loss. These initial symptoms typically develop over a period of years and may be subtle. The disease progresses at different rates in different people. Over time, people with the disease lose their ability to think and reason clearly, make judgments, solve problems, communicate, concentrate, remember useful information, and take care of themselves. As the disease progresses, changes in personality and behavior can develop. Individuals may experience anxiety, agitation, paranoia, delusions, and hallucinations.