A Finnish project (ALSOVA) has been following 240 patient-caregiver pairs, where the patient had very mild or mild Alzheimer's disease at the beginning of the study and had a family caregiver. A three-year follow-up of 115 patients has found that those diagnosed and treated very early were able to manage their everyday activities longer and suffered from less psychological and behavioral symptoms, compared to those diagnosed later.

http://www.eurekalert.org/pub_releases/2013-07/uoef-eda071813.php

[3574] Hallikainen, I., Hänninen T., Fraunberg M., Hongisto K., Välimäki T., Hiltunen A., et al.
(2013).  Progression of Alzheimer's disease during a three-year follow-up using the CERAD-NB total score: Kuopio ALSOVA study.
International Psychogeriatrics. 25(Special Issue 08), 1335 - 1344.