|Comparison of a normal aged brain (left) and the brain of a person with
|Symptoms||Decreased ability to
|Usual onset||Gradual |
|Duration||Long term |
|Prevention||Early education, prevent high blood pressure, prevent
|Frequency||46 million (2015) |
|Deaths||1.9 million (2015) |
Dementia is a broad category of
The most common type of dementia is
There is no known cure for dementia.
Globally, dementia affected about 46 million people in 2015.
 About 10% of people develop the disorder at some point in their lives.
 It becomes more common with age.
 About 3% of people between the ages of 65–74 have dementia, 19% between 75 and 84 and nearly half of those over 85 years of age.
 In 2013 dementia resulted in about 1.7 million deaths up from 0.8 million in 1990.
 As more people are living longer, dementia is becoming more common in the population as a whole.
 For people of a specific age, however, it may be becoming less frequent, at least in the developed world, due to a decrease in risk factors.
 It is one of the most common causes of
The symptoms of dementia vary across types and stages of the diagnosis.  The most common affected areas include memory, visual-spatial, language, attention and problem solving. Most types of dementia are slow and progressive. By the time the person shows signs of the disorder, the process in the brain has been happening for a long time. It is possible for a patient to have two types of dementia at the same time. About 10% of people with dementia have what is known as mixed dementia, which is usually a combination of Alzheimer's disease and another type of dementia such as frontotemporal dementia or vascular dementia.   Additional psychological and behavioral problems that often affect people who have dementia include:
When people with dementia are put in circumstances beyond their abilities, there may be a sudden change to crying or anger (a "catastrophic reaction"). 
Psychosis (often delusions of persecution) and agitation/aggression also often accompany dementia. 
In the first stages of dementia, the signs and symptoms of the disorder may be subtle. Often, the early signs of dementia only become apparent when looking back in time. The earliest stage of dementia is called
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In the early stage of dementia, the person begins to show symptoms noticeable to the people around them. In addition, the symptoms begin to interfere with daily activities. The person usually scores between a 20 and 25 on the
The symptoms of early dementia usually include memory difficulty, but can also include some word-finding problems (anomia) and problems with planning and organizational skills (executive function). One very good way of assessing a person's impairment is by asking if he or she is still able to handle his/her finances independently. This is often one of the first things to become problematic. Other signs might be getting lost in new places, repeating things, personality changes, social withdrawal and difficulties at work.
When evaluating a person for dementia, it is important to consider how the person was able to function five or ten years earlier. It is also important to consider a person's level of education when assessing for loss of function. For example, an accountant who can no longer balance a checkbook would be more concerning than a person who had not finished high school or had never taken care of his/her own finances. 
In Alzheimer's dementia the most prominent early symptom is memory difficulty. Others include word-finding problems and getting lost. In other types of dementia, like dementia with Lewy bodies and fronto-temporal dementia, personality changes and difficulty with organization and planning may be the first signs.
As dementia progresses, the symptoms first experienced in the early stages of the dementia generally worsen. The rate of decline is different for each person. A person with moderate dementia scores between 6–17 on the MMSE. For example, people with Alzheimer's dementia in the moderate stages lose almost all new information very quickly. People with dementia may be severely impaired in solving problems, and their social judgment is usually also impaired. They cannot usually function outside their own home, and generally should not be left alone. They may be able to do simple chores around the house but not much else, and begin to require assistance for personal care and hygiene other than simple reminders. 
People with late-stage dementia typically turn increasingly inward and need assistance with most or all of their personal care. Persons with dementia in the late stages usually need 24-hour supervision to ensure personal safety, as well as to ensure that basic needs are being met. If left unsupervised, a person with late-stage dementia may wander or fall, may not recognize common dangers around them such as a hot stove, may not realize that they need to use the bathroom or become unable to control their bladder or bowels (incontinent).
Changes in eating frequently occur. Caregivers of people with late-stage dementia often provide