There is a growing consensus that the amyloid plaques that are characteristic of Alzheimer's disease actually begin accumulating in the brain decades before symptoms like memory loss and personality changes begin to display themselves. This is one of the main reasons that the whole process of diagnosing Alzheimer's disease is set to change for the first time in over 25 years. If Alzheimer's disease is viewed as a disease with a lengthy (years or decades) preclinical phase, the new goal is to identify people at risk of developing the clinical phase of Alzheimer's disease in the future, so that drugs that can slow, modify, or halt the disease's progression will have the most effect.
One of the key driving forces behind this new perspective on Alzheimer's is the role of biomarkers, biological properties that can be detected and measured that indicate either normal or diseased processes in the body. Body temperature, for example, is a well-known biomarker for fever, and cholesterol level is a biomarker for heart disease. In Alzheimer's disease, several biomarkers have emerged that appear critical to early recognition: these include structural changes in the brain (like decreased size of the hippocampus), results of actual imaging of amyloid in the brain, spinal fluid abnormalities, and genetic markers.
One of the implications of viewing Alzheimer's disease as having a lengthy preclinical phase is the question of whether large scale screening tests should be done. Other diseases like breast cancer and prostate cancer have preclinical phases, but unlike Alzheimer's disease they also have effective early-stage treatments available now. An example of the debate over large-scale screenings for Alzheimer's that has been going on for some time now is available in a Washington Post article from December 2007. My feeling is that until we do have effective early stage treatments,most people would rather not want the anxiety that would accompany a positive screen for Alzheimer's disease. Since screening tests are not 100% accurate, others may feel falsely reassured if they screen as normal. Please share your comments below.