The epidemiology of Parkinson's disease

Abstract

The epidemiology of Parkinson's disease shows marked variations in time, geography, ethnicity, age, and sex. Internationally, prevalence has increased over and above demographic changes. There are several potential reasons for this increase, including the decline in other competing causes of death. Whether incidence is increasing, especially in women or in many low-income and middle-income countries where there is a shortage of high-quality data, is less certain. Parkinson's disease is more common in older people and men, and a variety of environmental factors have been suggested to explain why, including exposure to neurotoxic agents. Within countries, there appear to be ethnic differences in disease risk, although these differences might reflect differential access to health care. The cause of Parkinson's disease is multifactorial, and involves genetic and environmental factors. Both risk factors (eg, pesticides) and protective factors (eg, physical activity and tendency to smoke) have been postulated to have a role in Parkinson's disease, although elucidating causality is complicated by the long prodromal period. Following the establishment of public health strategies to prevent cardiovascular diseases and some cancers, chronic neurodegenerative diseases such as Parkinson's disease and dementia are gaining a deserved higher priority. Multipronged prevention strategies are required that tackle population-based primary prevention, high-risk targeted secondary prevention, and Parkinson's disease-modifying therapies for tertiary prevention. Future international collaborations will be required to triangulate evidence from basic, applied, and epidemiological research, thereby enhancing the understanding and prevention of Parkinson's disease at a global level.

Figure 1:. Simplified schematic of how risk and protective factors might determine neuropathology and the development of Parkinson’s disease

*While Parkinson’s disease is shown as developing in later life, the age of onset is variable and cases can develop disease at much younger ages.

Figure 2:. Hypothetical primary, secondary, and tertiary strategies to prevent, slow the onset of, and slow the progression of Parkinson’s disease across the life course

The horizontal line indicates a hypothetical threshold whereby decline in function is sufficiently severe to lead to a clinical diagnosis. (A) Normative trajectory of function that never results in clinical disease. (B) Extended plateau phase; decline is delayed and disease is diagnosed later in life. (C) Normative developmental phase, but rapid decline phase with earlier disease diagnosis. (D) Suboptimal developmental phase (lower plateau) followed by normative decline, leading to earlier disease diagnosis. *No assumptions have been made about the relative effectiveness of each strategy.