Semantic and episodic memory performance in Alzheimer's disease and vascular dementia
One of the most frequent differential diagnoses considered by clinicians working with geriatric populations involves the discrimination between vascular dementia (VAD) and Alzheimer's dementia (DAT). VAD and DAT patients often perform characteristically different on memory measures based primarily on the respective neural substrate involved in each disorder. The objective of this study was to determine whether semantic memory and episodic memory are impaired in vascular dementia, and to evaluate the utility of specific semantic and episodic memory measures in differentiating vascular dementia from dementia of the Alzheimer's type. Using tests of semantic and episodic memory, 44 DAT patients were compared to 44 patients having subcortical vascular changes using archival methodology. All participants were classified as having "mild" dementia, as indicated by Mini Mental Status Examination (MMSE) scores between 20 and 25. Results revealed that the VAD group performance was indeed better than that of the DAT patients on all three of the semantic memory tests included in the study (Information F (1,86) = 8.49, p <.004, Vocabulary F (1,86) = 7.79, p <.006, and Similarities F (1,86) = 7.66, p <.006 subtests of the WAIS-R). Comparison of the VAD and DAT groups on five episodic measures revealed that VAD patients performed better on three of the five measures (Logical Memory I F (1,86) = 20.57, p <.0001, and II F (1,86) = 33.21, p <.0001 from the WMS-R, and Recognition F (1,65) = 8.93, p <.004 from the Levin Selective Reminding Task). Discriminant function analysis revealed Logical Memory II as the best test measure discriminator of group membership, while education emerged as the best demographic discriminator of group membership. Additional analysis of storage versus retrieval scores from the Levin Selective Reminding Task revealed that the predicted difference between the two groups for retrieval performance was not confirmed. Results of the current study are compared and contrasted to previous related research, and the relevance of findings for diagnostic considerations is discussed. Overall results of the current study suggest that while semantic memory performance may be differentially impaired in DAT, as compared to VAD, episodic memory measures may be the best discriminators for the purposes of differential diagnosis.