Dementia is a loss of brain function that occurs with certain diseases. It affects memory, thinking, language, judgment, and behavior.

See also: Alzheimer's disease

Most types of dementia are nonreversible (degenerative). Nonreversible means the changes in the brain that are causing the dementia cannot be stopped or turned back. Alzheimer's disease is the most common type of dementia.

Lewy body disease is a leading cause of dementia in elderly adults. People with this condition have abnormal protein structures in certain areas of the brain.

Dementia also can be due to many small strokes. This is called vascular dementia.

The following medical conditions also can lead to dementia:

• Parkinson's disease
• Multiple sclerosis
• Huntington's disease
• Pick's disease
• Progressive supranuclear palsy
• Infections that can affect the brain, such as HIV/AIDS and Lyme disease

Some causes of dementia may be stopped or reversed if they are found soon enough, including:

• Brain tumors
• Changes in blood sugar, sodium, and calcium levels (see: Dementia due to metabolic causes)
• Low vitamin B12 levels
• Normal pressure hydrocephalus
• Use of certain medications, including cimetadine and some cholesterol-lowering medications
• Chronic alcohol abuse

Dementia usually occurs in older age. It is rare in people under age 60. The risk for dementia increases as a person gets older.