It must be emphasized that Alzheimer's disease is not the only type of dementia.

In more than 75% of patients, the memory impairments are due to Alzheimer's disease. In Lewy body dementia, which is accompanied by cognitive and/or further psychiatric symptoms, and in Parkinson's disease dementia, these develop only after the motor symptoms of the disorder have fully developed.
Gerhard Eschweiler and co-authors (Dtsch Arztebl Int 2010; 107[39]: 677-83) in their article introduce biomarkers that raise the probability of identifying Alzheimer's disease at the stage of mild cognitive impairment and up to five years before full-blown dementia to 80%.
Richard Mahlberg in an introductory editorial emphasizes that the attempts to find an exact differential diagnosis are not merely academic exercises, but that new developments of diagnosis-specific, differentiated interventions for the future depend crucially on a correct initial diagnosis.
Source-Eurekalert