About Alzheimer's Disease

In dementing illnesses, the biological changes occur in the brains of patients long before the appearance of symptoms. The definition 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.

Dementia is a general term for loss of memory and other mental abilities severe enough to interfere with daily life. Physical changes in the brain causes the dementia. 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.

Vascular dementia is widely considered the second most common type of dementia. It develops there is impaired blood flow to parts of the brain, which 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 effects become noticeable. This type used to be called “multi-infarct 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 has become increasingly common in advanced age. This belief is based on brain autopsies showing up to 45 percent of people with dementia having 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.

Frontotemporal dementia (FTD) is a rare disorder that affects the front (frontal lobes) and the sides (temporal lobes) of the brain. Since 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.

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.

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 that occurs when a 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,” and it tends to occur in much younger individuals, in some cases as early as their teens.

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, but 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.