Epidemiology

Despite being more common than other neurodegenerative disorders, PD is still generally considered rare. Methodological differences between studies, or poor methodology, complicate efforts to establish reliable estimates of PD incidence and prevalence, and the potential epidemiological role of ancestry and sex.

The mean age of onset of PD is about 65 years; prevalence increases with increasing age. Cases occurring in people aged 21-40 years are considered young-onset PD; patients younger than 21 years have juvenile parkinsonism.[2] Among residents of Olmsted County, Minnesota, the average annual incidence rate of parkinsonism was 0.8/100,000 person-years in people aged 0-29 years, increasing incrementally to 304.8/100,000 person-years in those aged 80-99 years.[3] A more recent review of prevalence of PD in Italy reported figures of 37.8 per 100,000 inhabitants in people aged 0-64 years, 578.7 per 100,000 in people aged 65-75 years, and 1235.7 per 100,000 in people aged 75 years and older.[4]

Approximately 6.1 million people worldwide had PD in 2016, compared with 2.5 million in 1990.[5] Age-standardised prevalence rates increased by 21.7% over the same period, indicating that the rise was not solely due to increased numbers of older people.[5] Some analyses report lower prevalence of PD in Africa and Asia than in western countries, but study heterogeneity necessitates caution when interpreting data.[5][6][7][8]

There are data to suggest that the incidence and prevalence of PD may vary by ethnicity.[9][10] In the US, PD appears to be substantially more common in white people, but socioeconomic and cultural factors may contribute to lower reduced rates of diagnosis in black, Asian, and Hispanic people.[10][11] Regional variations in PD prevalence have been reported in North America.[10][12]

Incidence and prevalence of PD appears to be greater in men than in women.[4][5][12][13] Age-standardised prevalence rates from 2016 indicate that PD is 1.4 times more common in men.[5] Differences between sexes relating to clinical presentation of motor and non-motor symptoms have been reported.[14]

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