Parkinson’s disease (PD) is known to cause neuropsychiatric symptoms (NPS). It has been established that the more advanced the motor stage of PD is, the more frequent and severe the NPS may be. However, the relationship between NPS and stage of cognitive decline is less well understood. This is important because the majority of people with PD will experience some degree of cognitive decline during the course of their disease, and there is a high risk of developing dementia (PDD). In non-PD populations there is a strong association between NPS and cognitive impairment and the same association may apply in PD. Consequently, the aim of this article is to provide a brief overview of NPS in PD from the perspective of stage of cognitive decline. We highlight studies that have demonstrated the increasing prevalence and severity of NPS with increasing cognitive impairment in PD. We point out the importance of apathy as a possible precursor to PDD. We also describe the negative impact of NPS and cognitive impairment on caregiver distress and quality of life. Finally, we have summarised findings from key studies of cognitive enhancers in PDD which have examined the effect of these treatments on NPS.
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