Multi-Infarct Dementia (MID)
After Alzheimer's disease, the nation's second leading cause of progressive mental deterioration is multi-infarct dementia. "Infarct" means tissue death, in this case, tissue in the brain. Brain tissues dies because the affected individual suffers a series of mini-strokes known as "transient ischemic attacks" (TIAs). Basically, multi-infarct dementia results from cumulative cerebral damage caused by little strokes that may go unnoticed.
Major strokes are hard to miss. More than 300 years ago, physicians noticed that some people who had not been struck on the head complained of sudden, severe head pain, as though they'd been bludgeoned, and soon afterward collapsed either dead or seriously disabled--unable to speak, or partially or completely paralyzed. The ailment occurred suddenly, like a "stroke of bad luck," so they named it "stroke."
According to the American Heart Association, stroke is the nation's third leading cause of death (after heart disease and cancer). Americans suffer about 500,000 strokes each year, and 150,000 stroke deaths. Approximately 3 million living Americans have had strokes. Some recover fully, but many suffer permanent disabilities, many of them dementing.
A stroke occurs when an artery in the brain becomes either blocked or ruptured and can't deliver oxygen and nutrients to brain tissue as it normally would. Deprived of nourishment, affected brain cells die. At the same time, the body parts those cells control become impaired, causing such stroke-related disabilities as paralysis, vision or speech difficulties, or an inability to recognize loved ones.
There are four major types of stroke, two caused by blocked blood flow in the brain ("ischemia"), and two by ruptured blood vessels that bleed ("hemorrhage"). The former, "cerebral thrombosis" and "cerebral embolism," together known as "ischemic stroke," account for about 80 percent of strokes. The latter, "cerebral hemorrhage" and "subarachnoid hemorrhage," collectively known as "hemorrhagic stroke," occur much less frequently, but are more likely to prove fatal.
Cerebral thrombosis is by far the leading cause of stroke, accounting for about 65 percent of what physicians call "cerebrovascular events" ("cerebro" means brain, "vascular" refers to the blood vessels). Cerebral thrombosis is the result of atherosclerosis, the same gradual narrowing of the arteries that causes heart attack, except that instead of restricting blood flow into the heart, the atherosclerosis associated with cerebral thrombosis affects blood flow through the brain. A key risk factor for cerebral thrombosis is high blood pressure, or hypertension. Other risk factors include: a family history, male sex, African-American race, diabetes, smoking, elevated cholesterol, and heart disease.
Just as the chest pain of angina precedes many heart attacks, about 10 percent of thrombotic strokes are preceded by mini-strokes, TIAs. TIAs occur when an internal blood clot temporarily blocks an already-narrowed artery in the brain, causing a brief period of substantially reduced blood flow, or "ischemia." TIAs are the most predictive risk factor for cerebral-thrombosis stroke. They multiply risk 10-fold. About one-third of those who experience a TIA have a stroke within five years. Half of post-TIA strokes occur within a year.
TIAs strike suddenly and usually don't last more than five minutes. They typically cause noticeable symptoms--numbness, fainting, dizziness, clumsiness, and/or loss of speech or vision, particularly in one eye. But some TIAs go unnoticed, or get dismissed as just "one of those things"--especially if they cause only momentary dizziness or fainting.
Even though most people recover from TIAs apparently completely, each episode causes some tissue death in the brain. Those who experience several TIAs ("multi-infarcts") may suffer enough cumulative brain damage to develop multi-infarct dementia.
Compared with Alzheimer's disease, which causes 50 to 60 percent of dementia, experts estimate that MID accounts for about 15 percent of cognitive deterioration (Gray, G.E. "Nutrition and Dementia," Journal of the American Dietetic Association (1989) 89:1795). MID usually develops more quickly than Alzheimer's disease, and frequently it is associated with stroke-related physical problems, for example, partial paralysis or slurred speech, which are not features of Alzheimer's. Nonetheless, the two conditions may be confused. In addition, Alzheimer's disease and multi-infarct dementia can co-exist. About one-fifth of those with senile dementia show signs of both conditions.
Fortunately, MID is both preventable, and to some extent, treatable--with low-dose aspirin (one-half to one standard tablet a day). Low-dose aspirin is not potent enough to cure a headache, but it helps prevent the internal blood clots that cause heart attack, cerebral thrombosis, and TIAs. A 1989 study at the Cerebral Blood Flow Laboratory at the Veterans Administration Medical Center in Houston showed that aspirin not only slows the progression of MID, but in some cases, reverses it. Researchers divided 70 MID sufferers, average age 67, into two groups. One received 325 mg of aspirin a day (one standard table).
The other took no medication. The participants' cerebral blood flow and mental faculties were evaluated yearly. Some MID sufferers in both groups improved, some stabilized, and some deteriorated. But those taking aspirin stabilized or improved three-to-one over the controls. The researchers concluded that the aspirin group, showed "significant improvement in cerebral blood flow and cognitive performance. Their quality of life and independence appeared to improve. Daily aspirin appears to stabilize declines or improve cognition in multi-infarct dementia." (Meyer, J.S. et al. "Randomized Clinical Trial of Daily Aspirin Therapy in Multi-Infarct Dementia," Journal of the American Geriatric Society (1989) 37:549.)
Today, low-dose aspirin is widely recommended as a stroke preventive for people who have had TIAs, and many neurologists also recommend it to treat MID. In cases where MID and Alzheimer's co-exist, low-dose aspirin can help minimize the MID part of the overall problem.
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