Fig. (1).

Distribution of the Major Age-Related Neurodegenerative Diseases. There are several different brain diseases that contribute substantially to cognitive impairment in the elderly. The weighted contributions shown on this pie chart are approximate and represent data collected from five different U.S. studies [8, 108-111]. Some other diseases that adversely affect cognition (including hippocampal sclerosis) affect many persons but are not discussed in this review. There is variation between studies due to population differences (e.g., mean age) and methodology. Thus, we have simplified these data for illustration. Note that AD accounts for more than one-half of cognitive impairment among American aged persons. In the “oldest old” (85+), some impact from cerebrovascular pathology is almost universal, and it is normal for the brains of individuals over the age of 80 to harbor more than one type of pathology.