In 1982 Professor Barry Reisberg proposed a Global Deterioration Scale that summarizes seven steps in the progression of AD and serves as an excellent means to describe its natural history (see Table 1).
The symptoms of AD are thus a combination of progressive decline in intellectual abilities and functional autonomy, very often with psychiatric features such as anxiety and depression (mostly in stages 3 and 4), followed by delusions, hallucinations, and wandering (mostly in stages 5 and 6). The latter symptoms cause a severe burden for the families and lead to nursing home placement in most countries. In the final stage of AD (stage 7), there are changes in motor tone and walking ability similar to those in Parkinson's disease. Death occurs within six to eight years after diagnosis, usually from pneumonia.
There is currently a great interest in the very early symptoms of AD, since early treatment with agents that modify the disease process can significantly delay progression from normal (stage 1) to minimal symptoms (stages 2 and 3), or from minimal symptoms to diagnosable AD (stage 4 and beyond). It appears that late onset depression with loss of interest, energy, or concentration; a long postoperative delirium; or subjective memory complaints with changes in abilities to handle finances, medication, phone, or transportation suggests the possibility of incipient AD.