Alzheimer's is a Very Gradual Process
The neurodegeneration state we call Alzheimer's is not a sudden onset at all, but rather builds up very slowly over time. This is becoming more clear as scientists more effectively detect biochemical markers early on: "Our findings show that beta-amyloid is associated with brain dysfunction - even in apparently normal elderly individuals ... PET is a highly specialized, noninvasive imaging technique that uses short-lived radioactive substances to produce three-dimensional images of those substances functioning within the body. ... We found that apparently normal elderly subjects with positive PIB PET scans do have mild - but significant - reduction in memory test scores, and this is related to the amount of amyloid present ... Besides providing an accurate diagnosis of early Alzheimer's disease, this research is helpful in providing the possibility of early diagnosis and intervention for individuals who are minimally impaired ... Additionally, 20 percent of the normal volunteers in our study whose average age was 72 had a positive scan. In subjects with mild cognitive impairment (MCI) - a condition that leads to Alzheimer's dementia in about 60 percent of cases - we found positive scans in 60 percent of the subjects. The amount of amyloid present, measured by the PIB scan, related to the severity of memory impairment in these subjects." Much like diabetes, early detection may mean a chance to change course.
Link: http://www.eurekalert.org/pub_releases/2007-06/sonm-wca052707.php