Alzheimer's disease is the most common form of dementia, a group of disorders that impairs mental functioning. (Dementia literally means loss of mentation, or thinking.) At the moment, Alzheimer's is progressive and irreversible. Abnormal changes in the brain worsen over time, eventually interfering with many aspects of brain function. Memory loss is one of the earliest symptoms, along with a gradual decline of other intellectual and thinking abilities, called cognitive functions, and changes in personality or behavior.
Alzheimer's advances in stages, progressing from mild forgetfulness and cognitive impairment to widespread loss of mental abilities. In advanced Alzheimer's, people become dependent on others for every aspect of their care. The time course of the disease varies by individual, ranging from five to 20 years. The most common cause of death is infection.