The prevalence of cognitive impairment and/or dementia in CBD is not established. Neuropsychological functions appear to be relatively preserved in the early stages of CBD, at least within an average of five years of diagnosis (188), with dementia emerging as a more common feature later in the disease course (189). Although the neuropsychological profile of CBD reveals both cortical and subcortical features (190), it is possible to differentiate CBD from AD and PSP (176,191). The neuropsychological profile associated with CBD is marked by significant executive dysfunction, which is comparable in severity to PSP, but relatively milder than is observed in patients with AD. Also evident in CBD is asymmetric apraxia (not evident in PSP or AD), alienhand sign (not reported in PSP or AD), impairment in motor programming and speed (similar to PSP but unlike AD), attentional dysfunction, and deficits in verbal fluency (comparable to AD). When aphasia is present it is most often of the nonfluent type (192). Memory impairment in CBD is characterized by deficient retrieval and encoding, but qualitatively and quantitatively different from AD, which is more likely to be marked by deficient consolidation and retention of information over time. Recall on remote memory tests is impaired, but unlike in AD, recognition is intact (193).
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