Multi-infarct dementia (MID), accounting for about 20 percent of all dementias, is caused by one or more small strokes that destroy or damage brain tissue. MID occurs most commonly after the age of 65, but it can also strike young or middle-age individuals with high blood pressure. Unlike Alzheimer's disease, more men than women are affected by MID.

But what causes Multi-infarct dementia?

The brain needs a well-regulated supply of oxygen-rich blood in order to function. If the supply is interrupted --- which is what happens during a stroke --- nerve cells in the area deprived of blood die, a process that is called infarction. A single stroke may cause severe damage to some cognitive functions, such as language ability or abstract thinking, but usually will not cause dementia; in fact, many people do recover, at least partially, from a single stroke. In MID, however, successive, multiple infarctions cause increasingly larger areas of cell death and damage. These small strokes or infarctions often occur without the patient experiencing any acute symptoms. When a sufficient area of the brain is damaged, dementia results.

In rare cases, illness produces such wide-spread brain damage over a few years that the symptoms and their progression are nearly identical to Alzheimer's. More often, however, multi- infarct dementia results in specific symptoms that point to the cause. For example, if the disease mainly affects the blood supply to the areas of the brain that govern mood, then mood changes will be the dominant symptoms. Victims of multi-infarct dementia usually are keenly aware of their mental deficits and regularly face bouts with anxiety and depression.

Here are some of the clinical symptoms that help physicians differentiate from Alzheimer's disease.

* MID comes on abruptly, rather than gradually, as in Alzheimer's (although a number of small strokes may occur before any symptoms of cognitive impairment are evident).

* It progresses in steps, as each successive stroke causes further deterioration.

* The individual still retains his or her unique personality (it is eventually lost in Alzheimer's), although subject to shifting swings of emotional moods --- for example, he or she may laugh, cry, or get angry in response to what appears to others to be minor provocations.

* The person with MID usually will have a history of hypertension or of previous strokes.

* Evidence of stroke will show on CT or MRI scans of the brain.

Because both Alzheimer's and MID are common conditions in the elderly, both illnesses can occur in the same individual, making it more difficult to establish an initial difficult diagnosis.

MID cannot be reversed. There is no specific treatment for it, other than the supportive measures for dementia.

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