Dementia is the loss of mental functions -- such as thinking, memory, and reasoning -- that is severe enough to interfere with a person's daily functioning. Dementia is not a disease itself, but rather a group of symptoms that are caused by various diseases or conditions. Symptoms can also include changes in personality, mood, and behavior. In some cases, the dementia can be treated and cured because the cause is treatable. Examples of this include dementia caused by substance abuse (illicit drugs and alcohol), combinations of prescription medications, and hormone or vitamin imbalances. In some cases, although the person may appear to have dementia, a severe depression can be causing the symptoms. This is known as pseudo-dementia (false dementia) and is highly treatable. In most cases, however, a true dementia cannot be cured.

Dementia develops when the parts of the brain that are involved with learning, memory, decision-making, and language are affected by one or more of a variety of infections or diseases. The most common cause of dementia is Alzheimer's disease, but there are as many as 50 other known causes. Most of these causes are very rare.

Because some causes of dementia can be cured or partially treated, it is very important that your doctor is thorough when making the diagnosis, so as not to miss potentially treatable conditions. The frequency of "treatable" causes of dementia is believed to be about 10%.

What Causes Dementia?

There are several things that could cause dementia:

Diseases that cause degeneration or loss of nerve cells in the brain such as Alzheimer's, Parkinson's and Huntington's.
Diseases that affect blood vessels, such as stroke, which can cause a disorder known as multi-infarct dementia.
Toxic reactions, like excessive alcohol or drug use.
Nutritional deficiencies, like vitamin B12 and folate deficiency.
Infections that affect the brain and spinal cord, such as AIDS dementia complex and Creutzfeldt-Jakob disease.
Certain types of hydrocephalus, an accumulation of fluid in the brain that can result from developmental abnormalities, infections, injury, or brain tumors.
Head injury -- either a single severe head injury or longer term smaller injuries, like in boxers.
Illnesses other than in the brain, such as kidney, liver, and lung diseases, can all lead to dementia.

Alzheimer's disease causes 50% to 60% of all dementias. But researchers have found that two nervous diseases, which were originally incorrectly diagnosed as Alzheimer's, are emerging as major causes of dementia: Lewy body disease and Pick's disease.

How Common Is Dementia?

Dementia caused by nervous system disease, especially Alzheimer's disease, is increasing in frequency more than most other types of dementia. Some researchers suspect that as many as half of all people over 80 years old develop Alzheimer's disease. Also, the increased incidence of AIDS dementia complex, which results from HIV infection, helps account for the increased dementia in recent history, although with the invention of newer and better drugs to treat HIV, the occurrence of AIDS-associated dementia is declining.

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