When in the course Parkinson disease (PD) does dementia or other cognitive impairment typically occur?

Updated: Aug 29, 2019
  • Author: Robert A Hauser, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Substantial cognitive impairment and dementia typically occur 8 years or more after the onset of motor features.

Dementia generally occurs late in Parkinson disease; substantial cognitive dysfunction within 1 year of onset of motor features suggests a diagnosis of Lewy body disease, a disease closely related to Parkinson disease and marked by the presence of cortical Lewy bodies. In the affected age group, comorbidity with other neurodegenerative disorders, particularly Alzheimer disease and cerebrovascular disease, is common. The relatively high prevalence of depression in patients with Parkinson disease is another confounder in the diagnosis of Parkinson disease dementia.

Executive function, short-term memory, and visuospatial ability may be impaired in patients with Parkinson disease dementia, but aphasia is not present. In a long-term Australian study that compared neuropsychologic measures between patients with Parkinson disease who had early dementia (< 10 years of disease onset) and those with late dementia, investigators reported that dementia in parkinsonism appears to occur at about age 70 years regardless of the time of onset of Parkinson disease. [34] However, although early and late dementia had similar effects in cognitive domains, individuals with early onset of parkinsonism had a preserved linguistic ability before the onset of dementia. [34]

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