Alzheimer's disease is a heterogeneous disease, in which patients do not follow a definitive clinical course. Three characteristic clinical presentations have been described by martin, each demonstrating a different primary behavioral impairment of memory, language, or visuo-spatial skills. Although there is no single presentation of the disease, various clinicians and researchers have described progressive stages of Alzheimer's disease following a behavioral paradigm, linguistic paradigm, and a neuropathological paradigm.