Cognitive and behavioural impairment in Parkinson's disease.

Although Parkinson's disease (PD) has been considered to primarily affect motor abilities, increasing emphasis is being placed on cognitive and behavioural impairment in this disorder. Depression, dementia, psychosis and impulse control disorders have a major impact on quality of life for both patients and families. This article reviews cognitive and behavioural disturbances in PD and their relation to affective and motor symptoms, treatment of dementia associated with PD, and treatment approaches to psychosis in PD. We also discuss similarities between the dementia of PD and dementia with Lewy bodies.