Dementia is a general term for a decline in mental ability severe enough to interfere with daily life. Dementia is a group of symptoms, while Alzheimer's is a disease. Dementia is the name for a group of brain disorders that make it hard to remember, think clearly, make decisions, or even control your emotions. What's the difference between dementia and Alzheimer's disease? Answer From Jonathan Graff-Radford, M. Dementia is caused by different diseases that affect the brain. According to the Centers for Disease Control (CDC), Alzheimer's disease is a common cause of dementia, causing as many as 50-70% of all.