The impact of dementia development concurrent with Parkinson's disease: a new perspective.

Dementia is the leading cause of disability worldwide among chronic diseases in the elderly and is a major contributor to mortality. Importantly, dementia that develops as a comorbid condition significantly compounds the burden of disease on the person, their caregivers and the health care system. Dementia is a frequent comorbidity of Parkinson's disease (PD) and about 80% of people with PD will develop dementia during the course of the disease. Incidence of dementia in PD ranges from 54.7 to 107.14 per 1000 person-years while point prevalence estimates range from 19.7 to 35.3%. The range in incidence and point prevalence can be attributed to varying diagnostic criteria, sample biases, and sample size. Nosologically, there is still disagreement on the origins of dementia in PD. Dementia development may be most often caused by the progression of PD-type pathology; however, the occurrence of Alzheimer's disease (AD)-type pathology suggests that an interplay exists between the genes and proteins associated with PD and AD. Furthermore, these genes and proteins may increase the risk and severity of dementia development in people with PD. Understanding the mechanisms of neurodegeneration in PD and AD may, therefore, improve efforts to manage and treat PD dementia. Given this, it is important to adequately define the frequency of PD dementia for informed decision making, particularly in the areas of aged-care and government health policy.