Multi-Infarct Dementia (MID)
Understanding the Second Leading Cause of Dementia
A son brings his mother, who is 73 years old, to a neurologist because he has noticed a gradual slowing of her thought and unsteadiness in her walk. On examination. she is found to have difficulties with planning, organization and memory. Her brain scan shows widespread stroke- related injury; deep within brain. She is diagnosed with vascular dementia.
What is vascular dementia, and what are the differences between it and Alzheimer's disease? Why is it important to determine what is causing such symptoms'?
This article will explore the answers to those questions and some of the new research that is improving our understanding of vascular dementia and ways to prevent it.
'A Cause of Mental Deterioration'
Vascular dementia is a descriptive term encompassing a wide range of diseases or disorders, the principal feature of which is marked loss of intellectual abilities resulting from some abnormality in blood flow to the brain.
German physician Alois Alzheimer is best known for his 1907 description of the disease later named after him. However he made other pioneering contributions as well, including thorough descriptions of several types of vascular dementia. Some of his contemporaries, including Russian physician Otto Binswanger also reported cases of dementia resulting from vascular causes
However, most of the advances in understanding the vascular causes of dementia were made after 1974. when Vladimir Hachinski, and colleagues proposed a set of criteria to help physicians decide whether a person with dementia has Alzheimer's disease or multi-infarct dementia, one of the most common forms of dementia.
Since then this set of criteria has been revised and agumented by the development of modern brain scanning techniques, such as CAT and MRI, which enable physicians to see structural changes including strokes in the brain of living patients. Research using these and other new techniques has shown that many different vascular disorders can cause dementia; however, two forms, multi-infarct dementia and Binswanger's disease, illustrate some of the general characteristics of vascular dementia.
Multi-Infarct Dementia Multi-Infarct dementia (MID) is caused by a number of strokes, often relatively small. The symptoms of patients with MID may appear very similar to those of patients with Alzheimer's disease (AD). Often the MID patient has trouble remembering things (especially recent events), finds it difficult to communicate or follow a conversation, or appears generally confused. In addition, a person with MID may experience symptoms such as hallucinations (seeing or hearing things that aren't real) delusions (firmly held false beliefs) or depression.
However, as Dr. Hachinski's diagnostic criteria underscored, there are often distinct differences between MID and AD. First and foremost, it is very unusual for an MID patient not to have risk factors for stroke, such as high blood pressure, heart disease, or diabetes. However, the presence of such risk factors in a person with dementia does not necessarily mean that MID is the cause.
Next, walking and other motor skills may be some of the first abilities impaired by MID.
And although some mental abilities of patients with MID may decline very gradually, an MID patient often experiences a more abrupt loss of intellectual skills. The course of the disease frequently progresses in "steps," the person's abilities remaining steady for a period of time and then declining rapidly. The reason for this variable and "stepwise" course is the underlying cause of MID: strokes. If further strokes do not occur, an MID patient's abilities may not continue to decline or, in some cases, may even improve.
Because specific areas of the brain play roles in specific abilities, the symptoms of MID depend greatly on where strokes occur in the brain. One patient may have several strokes in areas that control language, causing an early decline in understanding or initiating speech; another patient may become disoriented or lost because of a stroke in the parietal lobe, an area of the brain involved in spatial orientation.
Though considerable difference often occur between individual Alzheimer patients. Alzheimer's generally appears with certain distinguishing features. the earliest and most prominent of which is striking memory or, impairment. This pattern results from the characteristic degeneration of certain regions of the brain--regions associated with memory, and other ineffectual functions.
"In vascular dementia, there's no consistent pattern of symptoms, as there is in Alzheimer's." says Helena Chui, NID. an associate professor of neurology, at the University of Southern California School of Medicine in Los Angeles. "A stroke can occur anywhere in the brain. and therefore the symptoms. that result can be quite varied."
Indeed, the factors that lead to strokes in MID generally cause the forecast for MID patients to be worse than that for Alzheimer's patients. On average, MID patients live several years less than Alzheimer's patients after diagnosis, often dying from a heart attack or major stroke.
MID is often considered to be the typical vascular dementia, however, medical researches continue to reveal different types of vascular dementia with distinct features. One of these, Binswangers disease, is currently the focus of much controversy in the scientific community.
In I 894, Dr. Otto Binswanger identified 8 patients with the disease that now bears his name: it was once considered rare but is now being reassessed, and may be relatively common. Binswanger's disease is associated with stroke-related changes in the white matter deep within the brain.
Most Binswanger patients have a history of hypertension or heart disease. Symptoms often include difficulty walking, and lack of bladder control early in the course of the disease, with gradually progressive dementia developing later. Most Binswanger patients are diagnosed between the ages of fifty and seventy, and often have reduced survival because of vascular risk factors for stroke or heart attack.
A great debate now centers around the fact that white matter changes, the hallmark of Binswangers disease, have been observed in patients with many other diseases, including AD. In Addition, white matter changes are often found to a lesser degree in healthy elderly people.
"White matter changes are clearly important in producing cognitive impairment", says John Stilring Meyer, MD a professor of neurology at Baylor College, who points out that white matter changes are stroke-related changes but not necessarily full strokes. "However," he continues, "many people without cognitive impairment have white matter changes, so there may be some threshold. This is an area of great research interest."
Though the concept of Binswangers is currently being reconsidered, it is clear that patients with Binswangers Disease, like patients with other vascular dementias, may benefit by controlling risk factors for stroke.
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