Some people are still confused by the terms "dementia" and "Alzheimer's disease." People often believe that the two terms represent different conditions. However, Alzheimer's disease is a form or type of dementia. Dementia is not a specific disease itself. It is an overall term used to describe the symptoms and the effects of symptoms that happen because of certain types of diseases or medical conditions. Dementia happens when areas of the brain that are involved in functions such as learning, memory, language, and making decisions are affected by a disease, an infection, or some type of medical condition. The results of these conditions significantly interfere with the person's ability to function.
Although dementia is commonly associated with older people, dementia is not part of normal aging. Dementia is one of the major causes of being disabled throughout the world. The World Health Organization estimates that there are nearly 50 million cases of dementia worldwide, and that there are nearly 10 million new cases of dementia every year.
People that develop dementia may have difficulty with:
- Learning new information or recalling (remembering) information.
- Problems with attention and concentration.
- Expressing themselves verbally.
- Understanding spoken or written language.
- Making decisions.
- Understanding how objects in the environment are related to one another.
- Orientation such as not being able to remember the month, year, or where they are.
- Emotional functioning such as having issues with severe depression or anxiety.
The symptoms of dementia can appear gradually over time or may appear very suddenly as often happens after a stroke or some other medical condition that affects a person's brain. When two or more of these symptoms are severe enough to interfere with the person's daily functioning, they may have dementia. The most common early symptom of dementia is having problems learning information and remembering things. Other problems will often develop following issues with memory, although in some forms of dementia other problems such as problems with depression or with language may happen first.
The most common type of dementia is Alzheimer's disease, but there are many other known causes of dementia. Many of these causes of dementia can be very rare. Alzheimer's disease is believed to be the cause for 50% to 70% of all dementias. Other relatively common forms of dementia are:
- Vascular dementia which happens when there are disturbances with the veins and arteries in the brain (such as having a stroke) that lead to issues with thinking, remembering, etc. This type of dementia makes up about 15 to 20% of all dementias.
- Dementia with Lewy bodies is a form of dementia that may resemble Parkinson's disease at first and later may resemble Alzheimer's disease. Lewy bodies are protein deposits that develop in the nerve cells of the brain. When large numbers of these deposits develop in the areas of brain associated with memory and motor control the person may develop this form of dementia. This type may account for 10% to 20% of all dementias.
- Mixed dementias that happen when there is more than one cause of dementia. For example, a person who has Alzheimer's disease who then has had a series of strokes. It is believed that the vast majority of people who have dementia may have more than one cause. In this case, they have a major cause such as Alzheimer's disease and then have some other condition that could also contribute to their dementia such as a vascular problem.
- Reversible types of dementia (which may account for as high as about 20% of all dementias) such as the dementia that is associated with:
- severe depression
- not getting enough of certain vitamins (for example vitamin B12 or vitamin B1)
- normal pressure hydrocephalus (a blockage or buildup of the fluid that surrounds the brain)
- many others.
Other types of dementia account for a very small proportion of all types of dementia. These conditions include the dementia associated with HIV/AIDS, Parkinson's disease, frontotemporal dementia, and many other conditions. Some of these conditions are discussed in the following sections.