Alzheimer's Disease What is dementia? Dementia is a syndrome characterized by: 1. impairment in memory, 2. impairment in another area of thinking such as the ability to organize thoughts and reason, the ability to use language, or the ability to see accurately the visual world (not because of eye disease), and 3. these impairments are severe enough to cause a decline in the patient's usual level of functioning. Although some kinds of memory loss are normal parts of aging, the changes due to aging are not severe enough to interfere with the level of function. Many different diseases can cause dementia , but Alzheimer's disease is by far the most common cause for dementia in the United States and in most countries in the world. What is Alzheimer's disease? Alzheimer's disease (AD) is a slowly progressive disease of the brain that is characterized by impairment of memory and eventually by dis