Cognitive functioning in Alzheimer's and vascular dementia: a meta-analysis

Differentiating between Alzheimer's disease (AD) and vascular dementia (VaD) remains difficult but important if existing pharmacological treatments are to provide symptomatic relief in the case of AD or to alter disease progression in the case of VaD. Cognitive assessments play an important role in aiding diagnosis, despite a lack of clear evidence defining the cognitive abilities and tests that best distinguish between the two types of dementia. The current study therefore completed a meta-analysis of research comparing the cognitive abilities of persons diagnosed with AD and VaD. A comprehensive search was undertaken of the PubMed and PsychInfo databases, with 81 studies being eligible for inclusion. Weighted Cohen's d effect sizes, percentage overlap statistics, fail-safe Ns, and confidence intervals were calculated for all cognitive tests. Of the tests that were examined by more than one study, there was one test of perception and one test of verbal memory that showed large and significant group differences. There were an additional 12 tests that may prove useful. However, all cognitive tests were limited in their ability to discriminate between AD and VaD, suggesting that they should be used cautiously and only in conjunction with other information (imaging, medical history) when diagnosing patients.