Multi-Infarct Dementia
Alternate Names : MID
Definition
The most common form of vascular dementia, which is a deterioration in mental function caused by narrowing of blood vessels in the brain. This narrowing results from an accumulation of atherosclerotic plaques in these vessels. "Multi-infarct" means that there are numerous areas where this process has killed or damaged cells.
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Overview, Causes, & Risk Factors
MID affects approximately 4 out of 10,000 people. It is estimated that 10 to 20% of all dementias are caused by blood vessel (vascular) narrowing, making MID the third most common cause of dementia in the elderly, behind Alzheimer's disease and Dementia of Lewy Bodies (DLBD). MID affects men more often than women. The disorder usually affects older people, over 55 years, with the onset averaging around age 65.
The disorder is associated with atherosclerosis, a condition where fatty deposits occur in the inner lining of the arteries. Atherosclerotic plaque damages the lining of arteries. Platelets clump around the area of injury (a normal part of the clotting and healing process). Cholesterol and other fats also collect at this site, forming a mass within the lining of the artery. MID is not caused directly by the deposits of atherosclerotic plaque in the blood vessels of the brain, but by a series of strokes that leave areas of dead brain cells (infarction). This occurs when atherosclerotic plaques facilitate the formation of blood clots (thrombi) that block off the small blood vessels and prevent localized areas of the brain from receiving nutrients and oxygen from the blood flow that supplies them.
The consequences vary depending on the location and severity of the infarctions. Memory impairment is often an early symptom of the disorder, followed by judgment impairment. This often progresses in a stepwise manner to delirium, hallucinations and impaired thinking. Personality and mood changes accompany the deteriorating mental condition. Apathy and lack of motivation are common. Catastrophic reactions, where a person becomes withdrawn or extremely agitated, are also common. Confusion that occurs or is worsened at night is another common symptom.
Risk factors that make the development of MID likely include a history of stroke, hypertension, smoking and atherosclerosis. Atherosclerosis is the cause of numerous serious vascular problems, including heart attacks, cerebrovascular diseases, and peripheral vascular diseases (affected vessels are outside major organs, especially in the limbs), and may be associated with conditions such as diabetes mellitus, obesity, high cholesterol, and kidney disorders that require dialysis.
Some research suggests that MID may help cause or hasten the progression of Alzheimer's disease. MID may be misdiagnosed as Alzheimer's or found in addition to Alzheimer's disease. Since the difference cannot always be determined without brain biopsy and since there is little effective treatment for either condition, the distinction is mainly useful to researchers, not patients. However, once more carefully targeted therapies become available, the independent contribution of MID and Alzheimer's disease to the burden of dementia might become important to tailor these treatments accordingly in affected individuals.
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