Senile dementia/Alzheimer's type

Alternative names:

Alzheimer's disease; diffuse brain atrophy; primary degenerative dementia

Definition:

A disorder involving deterioration in mental functions resulting from changes in brain tissue. This includes shrinking of brain tissues, not caused by disorders of the blood vessels.

Causes, incidence, and risk factors:

Senile dementia/Alzheimer's type (SDAT) is the most common cause of intellectual decline with aging. The incidence is approximately 9 out of 10,000 people. This disorder affects women slightly more often than men and occurs primarily in older individuals.

The cause is unknown. Several factors are believed to be involved in the development of the disorder, but have not yet been proven. The neurochemical factors include lack of the substances used by the nerve cells to transmit nerve impulses (neurotransmitters), including acetylcholine, somatostatin, substance P, and norepinephrine. Environmental factors include exposure to aluminum, manganese, and other substances. The infectious factors include prion (virus-like organisms) infections that affect the brain and spinal cord (central nervous system). In some families (representing 5 to 10% of cases) there is an inherited predisposition to development of the disorder, but this does not follow strict (Mendelian) patterns of inheritance. The diagnosis is usually made by ruling out other causes of dementia.

Researchers have found that in families that have multiple members with Alzheimer's, there is a particular gene variation which is common to all of those with the disease. The gene, which produces a substance called apolipoprotein E4, is not said to cause the disease, it's presence simply increases the chances that the disease may eventually occur. There are many people who have the E4 gene and never become afflicted with Alzheimer's.

The onset is characterized by impaired memory, with progressive loss of intellectual function. There may be mood changes, changes in language capability, changes in gait, and other changes as the disorder progresses. There is a decrease in the size (atrophy) of the tissues of the brain, enlargement of the ventricles (the spaces within the brain), and deposits within the tissues of the brain.

The risk factors include age and family history of Alzheimer's disease.