What Is It?

Dementia is a pattern of mental decline caused by different diseases or conditions. Currently, 5 million people in the United States have dementia. Approximately 15 percent of people older than 65 are thought to have dementia. Alzheimer’s disease, the most common cause of dementia, will affect more than 12 million Americans in the next 20 years.

A person with dementia loses mental abilities. Memory loss usually comes first. Gradually the person becomes unable to perform basic mental and physical tasks. Typically, dementia develops slowly over months or years. The first symptoms are often subtle. Eventually, people with dementia can have significant memory loss. They also may lose their ability to speak, recognize other people, perform complex tasks or think critically.

Most commonly, dementia occurs when nerve cells (neurons) in the brain break down (degenerate), and connections between neurons are interrupted. These disruptions have a variety of causes, and usually cannot be reversed. Causes include:

  • Alzheimer’s disease causes about 40 percent to 45 percent of all dementias.
  • Vascular disease, such as stroke, causes about 20 percent.
  • Lewy body disease, which causes neurons in the brain to degenerate, causes another 20 percent of dementias.

Other conditions that can cause dementia include:

  • Creutzfeldt-Jakob disease
  • Traumatic Head injury
  • AIDS
  • Alcohol abuse
  • Degenerative diseases, such as Huntington’s disease and Pick’s disease
  • Brain abscess
  • Multiple sclerosis
  • More than 50 other rare degenerative conditions

In rare cases, dementia is caused by a treatable condition, and may be partially or entirely reversed if the condition is diagnosed and treated early:

  • Depression
  • Adverse reactions to drugs
  • Infections, such as syphilis or fungal meningitis
  • Metabolic conditions, such as deficiencies of vitamin B12, folate or thyroid hormone


Symptoms of dementia emerge slowly, get worse over time, and limit the person’s ability to function.

The initial symptom of dementia is memory loss. Although everyone has memory lapses from time to time, the memory loss of dementia is greater, and affects your ability to function. For example, forgetting where you put your car key is normal, but forgetting how to use the key is a possible symptom of dementia.

Often, someone with dementia recognizes that something is wrong, but fear may keep the person from seeking treatment. As the disease progresses, the person may become nervous, depressed or anxious about the symptoms.

Along with memory loss, a person with dementia may have trouble with complex mental tasks, such as balancing a checkbook, driving, knowing what day it is, and learning new things. Attention, judgment, problem solving, mood and behavior also may change. As the disorder progresses, the person may have difficulty speaking in full sentences, recognizing his or her surroundings, recognizing other people, or handling personal care, such as bathing. In some cases, a person with dementia may experience hallucinations, delusions, agitation, social withdrawal and insomnia.


The doctor’s first step in diagnosing the cause of dementia is to look at the person’s medical history and ask questions about when memory problems started and how quickly they got worse. This information, together with the person’s age, can point toward a likely diagnosis. For example, if the person is elderly and has had consistently worsening memory and other problems for several years, a doctor may suspect Alzheimer’s disease. If symptoms got worse rapidly, then Creutzfeldt-Jakob disease may be a likely cause. If the person has had a history of high blood pressure, diabetes and vascular disease, a doctor may suspect stroke.

To diagnose dementia, a doctor looks to see if a person’s memory gets progressively worse, along with at least one of the following:

  • Difficulty understanding or using language
  • The inability to perform a purposeful act or sequence of motor activities
  • The inability to recognize familiar objects or people
  • Difficulty doing such complex tasks as planning or organizing

Doctors test people by asking them to perform various tasks involving memory and attention. The doctor may ask the person what day and year it is or have the person count backwards from 100 by sevens (100, 93, 86, etc.). If the person answers correctly, dementia is not likely.

Laboratory tests can narrow down the possible causes. Some tests include:

  • magnetic resonance imaging (MRI) or Computed tomography (CT) scans — These create pictures of structures inside the head (similar to the way X-rays create images of bones). The pictures can reveal brain tumors and stroke. If these tests do not show any major abnormalities, the diagnosis could be Alzheimer’s disease.

  • Blood tests — These measure levels of thyroid hormone and vitamin B12, and may help to judge the person’s overall health.

  • Lumbar puncture (spinal tap) — This test, though rarely used, can evaluate dementias by examining spinal fluid for an infection in the central nervous system. It also may detect dangerously high fluid pressure inside the brain.

Expected Duration

In most cases, dementia gets worse and cannot be cured. A person with dementia may live for months, years or decades, depending on the underlying disease.

In the rare cases in which dementia is caused by a treatable condition, such as infection, metabolic disorder or depression, the dementia usually is reversed after treatment.


Most of the causes of dementia cannot be prevented. Good personal health habits and medical care, however, can prevent some types of dementia. Here are some things you can do:

  • Dementia caused by stroke — Monitor and control your blood pressure, exercise every day, and lower the fat in your diet to less than 30 percent of total calories.
  • Alcohol-related dementia — Limit the amount of alcohol you drink.
  • Traumatic dementia — Avoid Head injury by always using seat belts, helmets and other protective equipment.
  • Some infection-related dementias — Avoid high-risk sexual behavior.
  • Vitamin-deficiency dementia — See a dietitian for a diet assessment.
  • Hormone-related dementia — Ask your doctor to test whether your thyroid is functioning properly.

Keeping your mind active and your body fit may help to prevent mental decline and reduce or postpone memory loss. If you get a good education and continue to challenge your brain throughout life, you can help to protect your brain by building up connections between brain cells. If you do this, any brain injury that occurs, such as a stroke, may be less likely to cause devastating mental loss. Some scientists believe that taking vitamin E supplements daily (between 400 and 800 International Units) may help to keep your brain functioning well.


Treating dementia is complex and lengthy. The first step is to diagnose the cause, if possible, and then to treat it. Infections can be treated with antibiotics, alcohol-related dementia can be halted by not drinking, and depression can be treated with antidepressant medication. Drugs are available to control some symptoms of dementia, such as anxiety, agitation and insomnia (difficulty sleeping).

For most people with dementia, however, there is no effective treatment. In the early stages of Alzheimer’s disease, the prescription drug donepezil (Aricept) can improve memory temporarily in some people, but it does not stop the disease from getting worse.

People with dementia that cannot be reversed need care from doctors, nurses and social workers. This care can take place anywhere, including in a hospital, at home, in an assisted-living center, or in other types of facilities. Depending on the cause of the dementia, several specialists may be involved in care, including neurologists, psychologists, psychiatrists or geriatric doctors. Important aspects of care include:

  • Familiar surroundings, people and routines, because too much change can cause confusion and agitation
  • Bright, active environments to help focus the person’s attention and keep him or her oriented to the environment
  • Safe environments so that the person cannot be hurt or get lost if he or she wanders away
  • Physical exercise to improve balance and general good health
  • Appropriate therapies, including music, art and occupational therapy, to provide stimulation and improve control of muscles

When To Call A Professional

Call your doctor if you have any concern about your memory, or if you or a loved one is having more difficulty recently with any of the following:

  • Learning and remembering new information
  • Handling complex tasks, such as preparing a meal
  • Reasoning, such as knowing how to organize shopping
  • Orientation, such as knowing the day of the week or the time of day
  • Language, including finding words to express thoughts

A person with dementia may also exhibit the following types of behaviors:

  • Changes in mood behavior, such as irritability
  • Placing everyday objects in odd places, such as putting a hat in the microwave
  • Forgetting the day, month, time or location
  • Loss of desire to initiate activities or be as active as usual


The outlook for dementia depends on the cause and can vary by individual. For example, early treatment of dementia caused by a vitamin deficiency can lead to full recovery of memory. If stroke is the cause, the person’s memory loss can remain stable for years. Drugs may slow the rate of decline for some people with Alzheimer’s disease. In many cases, however, the disorder gradually gets worse. Depending on the cause, the person’s age, general health, and the availability of treatments, life expectancy can be as short as a few months or as long as 15 to 20 years.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.