Alzheimer's disease: definition

Alzheimer's disease (AD) is a neurodegenerative disorder mainly characterized by the progressive and irreversible loss of nerve cells (neurons) located in specific brain areas: the hippocampus and the polymodal association areas.

AD is a disease that attacks the brain and results in impaired memory, thinking and behavior.

AD is the most common form of dementia.The degenerating process and the resulting neuronal loss lead first to memory impairment and later to dementia. At the end of the disease, most, if not all the cortical brain areas, as well as many subcortical nuclei, are heavily filled with two different types of lesions: amyloid plaques and neurofibrillary tangles.

In degenerating neurons, the microtubule network is transformed into abnormal filaments made up of pathological Tau proteins.

Dementia is a loss of intellectual function (thinking, remembering and reasoning) so severe that it interferes with an individual's daily functioning and eventually results in death.

AD is the fourth leading cause of death in adults, after heart disease, cancer and stroke. Men and women are affected almost equally. The disease was first described by Dr. Alois Alzheimer in 1906. Since then, researchers have developed a deeper understanding of the changes in the brain (plaques and tangles) and behavioral changes that characterize the disease. Identified risk factors are age and family history. Most people diagnosed with AD are older than age 65; however, AD can occur in people in their 40s and 50s.

Symptoms: Symptoms of AD can include gradual memory loss, decline in the ability to perform routine tasks, disorientation, difficulty in learning, loss of language skills, impairment of judgment and planning and personality changes. The rate of progression varies from person to person. The time from the onset of symptoms until death ranges from 3 to 20 years; the average is 8 years. Eventually persons with AD become totally incapable of caring for themselves.

What is Alzheimer's disease?

It is one of several neurological diseases which cause dementia, and is the fourth largest killer in the United States. Approximately four million Americans currently have AD, and that number is estimated to increase to at least seven million in the United States by the early 21st century. Alzheimer's disease is thought to affect five percent of people over age 65 and 20 percent of people over age 80.

Because there are many diseases that can cause symptoms similar to Alzheimer's disease, a thorough medical evaluation is necessary to make a diagnosis:

- The evaluation for a probable diagnosis of Alzheimer's disease requires blood tests and often a brain neuroimaging procedure such as a computed tomography (CAT or magnetic resonance image (MRI) scan. However, there is no simple definite test to diagnose Alzheimer's disease.

- A definite diagnosis is only possible with an autopsy to identify the characteristic neurofibrillary tangles and neuritic plaques of degenerating neurons. These appear in the areas of the brain with important roles in memory, learning and intellectual functioning.

The course of Alzheimer's disease varies tremendously, but the average duration of the illness is 10 to 12 years. Unlike some diseases that can have remissions, Alzheimer's disease is always progressive.