Merck Manual

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The Manual's Editorial Staff

Reviewed/Revised Dec 2022
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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.

What causes dementia?

Dementia is a brain disorder. It may have no specific cause, or it may 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 being 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 having 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 Others become withdrawn and depressed.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:

Care for caregivers

Caring for people with any type of dementia is stressful and demanding. Caregivers may become depressed and exhausted, often not taking care of their own mental and physical health. It's important for caregivers to:

  • Learn how to meet the needs of people with dementia and what to expect from them

  • Seek help when needed, such as from day-care programs, visits by home nurses, housekeeping help, live-in assistance, counseling, and support groups

  • Take time to care for themselves, including spending regular time with friends and on hobbies and activities

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