Cognitive impairment in Parkinson's disease

Although Parkinson's disease (PD) has been regarded as a condition in which disordered movement is the main feature there is now evidence that a substantial proportion of sufferers also show cognitive impairment. Some subjects are so severely affected that their impairment fulfils criteria for dementia. Research in the field presents many methodological problems: these are reviewed together with the nature, origins and neuropathology of impairment. PD has been the subject of research partly because it provides a model for the examination of brain function.The occurrence of dementia in PD is one of the factors that has lead to the re-examination of the nature of neurodegenerative disorders more widely. Cognitive impairment in PD has major implications for clinical management and for survival.