The difference between Alzheimer's and dementia is that the former is a specific disease while the other is an umbrella term for a series of symptoms. Because Alzheimer's is difficult to definitively diagnose, most living patients in whom Alzheimer's is suspected are clinically defined as having "Alzheimer's-like dementia." There are, however, many other causes of dementia.
Dementia
Dementia refers to a cluster of symptoms. Some of the most common symptoms of dementia include memory loss, problems with language and communicating, as well as trouble planning. Other symptoms can include changes in personality, paranoia, hallucinations and difficulty in behaving in a socially appropriate way.
Alzheimer's Disease
Alzheimer's disease is the most common form of dementia. Although it is not entirely understood how the disease occurs, it is understood that it relates to a problem with a protein also known as A-Beta. In Alzheimer's disease, this protein forms large clumps of protein clusters called amyloid fibrils. It is not understood what role these fibrils have in the development of the dementia that Alzheimer's causes.
Vascular Dementia
The second most common type of dementia is called vascular dementia. It is caused by small strokes that kill off small sections of brain cells. It can also be caused by the narrowing of blood vessels that supply the brain. Some of the specific features of vascular dementia include problems with walking or muscle control, as well as urinary incontinence. Another feature of this form of dementia is that the symptoms progress in a "step-wise" manner (meaning that the symptoms will stay the same for a period of time and then suddenly get worse).
Other Forms
There are many other forms of dementia. Parkinson's disease can, in its later stages, cause dementia. Another form is called "dementia with Lewy bodies" which is marked by the early appearance of hallucinations and the patient alternating between periods of confusion and lucidity. Fronto-temporal dementia, on the other hand, causes severe deficiency in being able to behave appropriately in social settings and impulsive behavior.
Diagnosis
Although the cause of dementia can often be inferred from the onset and progression of symptoms, in many cases the type of dementia can be definitively diagnosed only after the patient has died, by looking at the brain. The brain of a patient with vascular dementia will have multiple small areas of dead brain tissue. Other forms of dementia can be diagnosed by looking at sections of brain tissue under a microscope.
