Subtypes of Alzheimer's dementia: a conceptual analysis and critical review.

Criteria necessary for establishing the existence of qualitatively-different subtypes of a disorder are proposed. A review is made of the existing literature on Alzheimer's Dementia which proposes subtypes on the basis of either psychological or neuropathological data. It is concluded that, as yet, this research has not met the criteria for establishing qualitatively-different subtypes. However, Alzheimer's Dementia does seem to show quantitative variability in a number of respects and this appears to be related to factors of aetiological significance. The possibility that this quantitative variability could provide the basis for subtyping is discussed.