It was not so many years ago that a diagnostic approach to dementias was limited to the exclusion of potentially reversible causes. It is becoming increasingly clear that clinicians now need to be able to differentiate not only between reversible and irreversible causes but also between the primary degenerative dementias themselves. The past decade has seen great advances in our understanding of the basic science of the dementias, particularly Alzheimer's disease, bringing us not only a theoretical basis for different symptomatic conditions in different dementias, but also the promise of future therapies that may act directly on the molecular underpinnings of these diseases.

If clinicians are to be able to make these clinical distinctions and initiate appropriate therapy, then …