James Parkinson in his original observations on Parkinson's disease (PD) commented mainly on tremor and gait abnormality (1); however, it has become increasingly evident that PD patients can have cognitive and behavioral changes, and that these changes, most notably psychosis and dementia, can affect motor function. Furthermore, pharmacotherapy of psychosis and dementia can limit optimal treatment of the motor symptoms through dopamine antagonism and can even contribute to cognitive and behavioral dysfunction in PD. This makes it complicated to differentiate which features are medication side effects and which are intrinsic to PD.
It is essential to identify both psychosis and dementia in PD. Those with concomitant dementia are more prone to the development of dopamine-induced confusion, agitation, and psychosis, limiting treatment of the motor symptoms. Psychosis in PD is a risk factor for nursing home placement (2,3) and is associated with a higher mortality rate (4,5). Moreover, psychosis is the single greatest stress for caregivers. Dementia in PD also contributes to caregiver stress (6) and leads to a more rapid motor and functional decline (7,8), early institutionalization (2,9), and increased mortality (10-12). As the manifestations of psychosis and dementia are potentially treatable, recognition and treatment may enable the PD patient to live at home for a longer period and decrease caregiver stress.
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