Neuropsychological deficits in vascular dementia in relation to Alzheimer's disease: reviewing evidence for functional similarity or divergence.

The hypothesis that vascular dementia (VAD) may be associated with a specific pattern of neuropsychological dysfunction as compared to Alzheimer's disease (AD) is reviewed. The empirical findings were evaluated with regard to methodology, most importantly the comparability between groups regarding demographic variables and severity of dementia. They were also classified according to the cognitive and sensory-motor functions affected. No consistent differences were found between VAD and AD patients in neuropsychological performance testing general cognitive functioning, syntax, verbal comprehension, visuospatial tasks, and primary as well as semantic memory, indicating a functional similarity between VAD and AD. However, inferior performance was found for VAD in executive functioning, verbal fluency, attention, and motor performance. Superior performance for VAD was found in naming and with regard to intrusion errors. The findings on episodic memory were inconclusive. These results should be considered in light of possible selection bias due to the fact that all studies used a hospital-based sample of subjects and not subjects from the community. Bias may also arise from the variations in lesion site, size, number, and timing between different VAD groups. Third, the risk of confounding errors due to a lack of comparability between etiological groups in terms of demographic variables as well as cognitive decline cannot be excluded. Future studies should take into account variation in the severity of cognitive decline, variation regarding lesion characteristics, etiological factors, and subtypes of VAD in order to increase our knowledge about the functional features of VAD.