Prevalence rates of dementia in PSP range from 50% to 80%, but some authors contend that these numbers reflect over-diagnosis due to bradyphrenia, emotional problems, and visual dysfunction that accompany PSP. Cognitive deficits are seen in approximately 50% of patients with PSP (172), with the neuropsychological profile being typical of diseases with subcortical involvement, including slowed information processing, executive dysfunction, and information retrieval deficits (173). As compared to patients with PD, cognitive slowing and executive dysfunction in PSP emerges earlier in the disease course, is more severe, and progresses more rapidly (174-177), and this differential executive dysfunction may reflect radiographically demonstrated differences in frontal atrophy between the two conditions (178). Executive dysfunction in PSP may also differ qualitatively from that in PD (179). Memory and attention are relatively intact in PSP, although retrieval deficits and accelerated rates of forgetting may be present (180,181). The early presence of cognitive impairment distinguishes PSP from MSA (182).
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