Redefining Amnestic Mild Cognitive Impairment as an Early Form of Alzheimer's Disease Based on Assessment of Memory Systems

Background: It has been suggested that mild cognitive impairment (MCI) can be used to identify patients at risk of developing clinical stages of Alzheimer's disease (AD). Objective: The aim of this study was to describe the characteristics of amnesic syndrome of dementia of the Alzheimer's type (DAT) as a continuous degenerative process from normality to amnesic syndrome and provide a classification of the degrees of amnesia. Methods: Of 3,800 new incidental cases at the Memory Clinic, 747 were classified as non-demented patients. A 96-month follow-up study was conducted. We described and compared longitudinal outcomes from normality to amnesic syndrome based on immediate memory, verbal learning, free recall, and recognition using the memory scale from the Basic Neuropsychological Battery, version D (BNB-D) and created a new classification of memory impairment. Results: Based on differences observed in this longitudinal study, we classified patients in four memory stages: M1, Normal episodic memory; M2, mild impairment in learning and/or free recall; M3, clear impairment in learning and/or free recall; and M4, complete amnesic syndrome. With this new amnesia classification, we studied the chronological progression of all patients diagnosed without dementia from baseline to DAT conversion using the Kaplan-Meier estimator of survival probability (Log Rank/Mantel Cox comparison chi(2) = 171.84, p = 0.001). Conclusion: This new classification of memory impairment can help increase the prediction certainty of conversion from amnestic MCI to AD and improve research on AD biomarkers and their relationship with memory as the principal manifestation of AD.