About Alzheimer's Disease And Dementia
Dementia is a general term for loss of memory and other mental abilities severe enough
to interfere with daily life. It is caused by physical changes in the brain.
Alzheimer's disease is the most common type of dementia, accounting for 50 to 70
percent of cases. Other causes of dementia include vascular dementia, mild cognitive
impairment, mixed dementia, dementia with Lewy bodies, Parkinson's disease,
frontotemporal dementia, Creutzfeldt-Jakob disease, normal pressure hydrocephalus,
Huntington's disease, and Wernicke-Korsakoff syndrome.
Alzheimer's disease (AD) is a neurodegenerative disorder currently affecting approximately
4.5 million individuals in the United States. It is a disorder characterized by the
accumulation of plaques and tangles in the brain. The neuropathology typically begins
in the entorhinal cortex of the hippocampus. Since this area is critical for memory,
early memory impairment is the leading clinical symptom. As the disease spreads to other
portions of the brain, other cognitive functions become disturbed.
Current treatments for AD include the use of cholinesterase inhibitors and memantine,
an N-methyl D-aspartate (NMDA) antagonist. While these drugs are capable of producing drug
placebo differences in treated populations, neither class of agents has been demonstrated
to either slow the rate of decline or prevent progression of disease.
Vascular dementia is widely considered the second most common type of dementia.
It develops when impaired blood flow to parts of the brain deprives cells of food
and oxygen. The diagnosis may be clearest when symptoms appear soon after a single
major stroke blocks a large blood vessel and disrupts the blood supply to a significant
portion of the brain. This situation is sometimes called “post-stroke dementia”.
There is also a form in which a series of very small strokes, or infarcts, block small
blood vessels. Individually, these strokes do not cause major symptoms, but over time
their combined effect becomes noticeable. This type used to be called “multi-infarct
Mild Cognitive Impairment
In dementing illnesses, the biological changes occur in the brains of patients long before
the appearance of symptoms. The concept of mild cognitive impairment (MCI) was developed
as an attempt to recognize Alzheimer's disease (AD) in its very earliest clinical expression
in an individual who is destined to develop a progressive dementia at a later point in time.
Interventions might then be developed to improve the memory impairment or to delay further
deterioration to dementia.
Mixed dementia is a condition in which AD and vascular dementia occur at the same time.
Many experts believe mixed dementia occurs more often than was previously realized and
that it becomes increasingly common in advanced age. This belief is based on brain
autopsies showing up to 45 percent of people with dementia have signs of both Alzheimer's
and vascular disease.
The concept of mixed dementia is clinically important because the combination of the
two diseases may have a greater impact on the brain than either by itself.
Dementia with Lewy Bodies
Dementia with Lewy bodies is characterized by abnormal deposits of a protein called
alpha-synuclein that form inside the brain's nerve cells. These deposits are called
“Lewy bodies” after the scientist who first described them. Lewy bodies have been
found in several brain disorders, including
dementia with Lewy bodies, Parkinson's disease and some cases of Alzheimer's.
Parkinson's disease begins by affecting movement, resulting in tremors and shakiness,
stiffness, difficulty with walking and muscle control, lack of facial expression and
impaired speech. Parkinson's is another disease in which Lewy bodies are found in the brain.
Many individuals with Parkinson's develop dementia in later stages of the disease.
Frontotemporal dementia (FTD) is a rare disorder that affects the front (frontal lobes)
and the sides (temporal lobes) of the brain. Because these regions often, but not always,
shrink, brain imaging can be useful in diagnosis. There is no specific abnormality
associated with all cases of FTD. In one type called Pick's disease, there
are abnormal microscopic deposits called Pick bodies, but these are not always present.
Creutzfeldt-Jakob disease (CJD) is a rare, rapidly fatal disorder affecting about 1 out
of 1 million people per year worldwide. It usually affects individuals older than 60.
CJD is one of the prion diseases. These diseases occur when prion protein, which is
present throughout the brain, begins to assume an abnormal three-dimensional shape.
This shape gradually triggers the protein throughout the brain to fold into the same
abnormal shape, leading to increasing damage and destruction of brain cells. Recently,
“variant Creutzfeldt-Jakob disease” was identified as the human disorder believed to
be caused by eating meat from cattle affected by “mad cow disease.” It tends to
occur in much younger individuals, in some cases as early as their teens.
Normal Pressure Hydrocephalus
Normal pressure hydrocephalus (NPH) is another rare disorder in which fluid surrounding
the brain and spinal cord is unable to drain normally. The fluid builds up, enlarging
the ventricles (fluid-filled chambers) inside the brain. As the chambers expand,
they can compress and damage nearby tissue. The “normal pressure” refers to the fact
that the spinal fluid pressure often, although not always, falls within the normal
range on a spinal tap.
Huntington's disease is a fatal brain disorder caused by inherited changes in a single gene.
These changes lead to destruction of nerve cells in certain brain regions. Scientists
identified the gene in 1993. Anyone with a parent with Huntington's has a 50 percent
chance of inheriting the gene, and everyone who inherits it will eventually develop
the disorder. In about 1 to 3 percent of cases, no history of the disease can be found
in other family members.
Wernicke-Korsakoff syndrome is a two-stage brain disorder caused by a
deficiency of thiamine (vitamin B-1). Thiamine helps brain cells produce
energy from sugar. When levels of the vitamin are too low, cells are unable
to generate enough energy to function properly.
Wernicke encephalopathy is the first, acute phase and Korsakoff psychosis is the long-lasting,
chronic stage. The most common cause is alcoholism, but the syndrome can also be associated
with AIDS, cancers that have spread
through the body, very high levels of thyroid hormone, and certain other conditions.
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Copyright 2008 Regents of the University of California.
Copyright 2008 Regents of the University of California.