Merck Manual

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Quick Facts



The Manual's Editorial Staff

Last full review/revision Apr 2019| Content last modified Apr 2019
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What is dementia?

Dementia is a brain problem that makes it hard to remember, think, and learn. Most dementia begins little by little and starts after age 65.

  • It’s normal for the brain to change with age, but dementia isn't a normal part of getting older

  • Most dementia is caused by Alzheimer disease, a brain disorder

  • Symptoms usually start with forgetting recent events and getting lost easily

  • Symptoms get worse over the next 2 to 10 years to the point where help is needed with daily tasks, such as eating and walking

  • Doctors will try to slow memory loss as long as possible and help keep the person with dementia safe

What causes dementia?

Dementia is a brain disorder. It may have no specific cause or be caused by many disorders.

Most dementia in older people is caused by

Other brain problems that can cause dementia include:

Some things can make dementia worse:

  • Other health problems, such as heart failure and thyroid disorders

  • Alcohol

  • Medicines, such as sleeping pills, cold medicine, and medicine for anxiety

What are the symptoms of dementia?

Dementia causes problems with:

  • Memory

  • Using language

  • Personality

  • Thinking clearly

These problems make it hard to do normal daily tasks, such as shopping, making meals, and managing money. People also may have trouble behaving appropriately.

Symptoms get worse as time goes by.

Early symptoms of dementia:

  • Forgetting things that just happened

  • Forgetting where things are

  • Having trouble finding the right word to say and understanding what others say

  • Forgetting to pay bills

  • Having more trouble than usual with numbers

  • Getting lost when driving in familiar areas

  • Being more emotional, such as quickly switching from being happy to sad

Family and friends often notice that people don't seem like themselves. At first, the differences may be hard to spot. Sometimes people themselves are the first to notice they're having trouble with things. Such difficulties often make them frustrated and upset.

Middle symptoms of dementia:

  • Getting lost at home, such as trouble finding the bathroom or bedroom

  • Not recognizing familiar people and things

  • Being easily confused and unable to learn new information or follow simple directions

  • No longer safe to drive

  • Needing help with bathing, dressing, and eating

  • Not understanding normal conversation

  • Doing unusual things, such as yelling, undressing in public, hitting, and repeating questions

  • Having problems falling and staying asleep

Personality changes become more severe. People with dementia may be fearful and suspicious. Some are irritable and hostile. Others become withdrawn and depressed.

Late symptoms of dementia:

  • Losing all memory for recent and past events

  • Being unable to understand conversation

  • Not knowing close family or their own face in the mirror

  • Not being able to walk, feed themselves, or do other daily tasks

In late dementia, people lose almost all brain function. They can't get out of bed or even move. Eventually, they can't even swallow food that's placed in their mouth.

How can doctors tell if someone has dementia?

Doctors will ask people and their family members questions about symptoms. They’ll also do memory and other brain tests.

To see if another health problem is causing the dementia, doctors will do a physical exam and blood tests. They also do imaging tests such as a computed tomography (CT) or magnetic resonance imaging (MRI) to look for abnormalities of the brain.

How do doctors treat dementia?

Doctors may:

  • Treat other health problems that caused the dementia or make it worse

  • Stop any medicines that make dementia worse

  • Give medicine to slow memory loss and help with behavior changes

  • Explain the importance of a daily routine for bathing, eating, sleeping, and exercise

  • Help create a plan for safety at home (for example, putting up signs with reminders like "remember to turn off the stove" and scheduling visits from family members or friends)

  • Ask about end-of-life wishes, such as moving to a nursing home and whether to have CPR or be put on a ventilator

Creating a Beneficial Environment for People with Dementia

People with dementia can benefit from an environment that is:

  • Safe: Extra safety measures are usually needed. For example, large signs can be posted as safety reminders (such as “remember to turn the stove off”), or timers can be installed on stoves or electrical equipment. Hiding car keys may help prevent accidents, and placing detectors on doors may help prevent wandering. If wandering is a problem, an identification bracelet or necklace is helpful.

  • Familiar: People with dementia usually do best in familiar surroundings. Moving to a new home or city, rearranging furniture, or even repainting can cause problems.

  • Stable: Establishing a regular routine for bathing, eating, sleeping, and other activities can give people with dementia a sense of stability. Regular contact with the same people can also help.

  • Full of reminders: A large daily calendar, a clock with large numbers, a radio, well-lit rooms, and a night-light help people be aware of when and where they are. Also, family members and caregivers can always say who they are each time they see the person. They can also make frequent comments that remind people with dementia of where they are and what's going on.

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