Cognitive differences between patients with progressive supranuclear palsy and Alzheimer's disease.

Sixteen patients with dementia of the Alzheimer type (AD) and nine patients with Progressive Supranuclear Palsy (PSP) were administered a battery of neuropsychological tasks that assessed a cross-section of cognitive abilities. The subjects were equated in terms of overall level of impairment. There was no difference between the groups on the WAIS subtests that were administered (Vocabulary, Digit Span Forward, Similarities, Block Design). There was a striking difference between the AD and PSP patients on tests of verbal and nonverbal memory, as assessed by the Wechsler Memory Scale. The memory performance of the PSP patients did not, in fact, differ from a group of normal controls. In addition, there was a double-dissociation between the AD and PSP patients on tasks that evaluated naming and verbal fluency.