Original articleRisk tables for parkinsonism and Parkinson's disease
Introduction
Several studies have provided prevalence or incidence rates for Parkinson's disease (PD) 1, 2, 3, 4, 5, 6. However, because incidence rates express the probability of developing a disease over a short unit of time and prevalence figures are affected by survival, these indices convey little information about the risk of developing PD over a longer time period (e.g., between age 50 and 70 years) or over the entire lifetime of an average person in a population. The cumulative incidence provides an estimate of the risk of developing a disease over a long time; however, this index does not take competing causes of death into account. By contrast, the remaining lifetime risk of developing a disease after a given age is the estimate of the risk of ever becoming affected by the disease after having survived free of the disease up to that age 7, 8, 9. By combining the incidence rates of a disease with the mortality rates for all causes in the population, this statistic takes competing risks of death (or life expectancy) into account. Remaining lifetime risks have been used extensively in the cancer literature. Only recently, similar risks were estimated for dementia and Alzheimer's disease 10, 11, 12. To our knowledge, there are no data available on the remaining lifetime risks of parkinsonism and PD.
Our objective was to estimate the risks of parkinsonism and PD at different ages by means of a life table approach and to present them in a table format for easy consultation. Estimates of the risk of developing parkinsonism or PD are important in clinical practice, epidemiologic research, and public health.
Section snippets
Methods
The risks of developing parkinsonism and PD presented in this paper were obtained by combining two sources of data. First, we used previously reported age- and sex-specific incidence rates of parkinsonism and PD from Olmsted County, MN, for the period 1976–1990 [3]. Second, we used the Minnesota life tables for 1989–1991 based on the 1990 census data [13].
Results
Table 1 shows the incidence rates of parkinsonism and PD in Olmsted County, MN, for the period 1976–1990 overall and for men and women separately. The incidence rates of parkinsonism and PD increased steeply with age after 50 years (however, they declined in men after age 80 years for PD). Incidence rates were consistently higher in men than in women at all ages for both parkinsonism and PD.
Table 2 shows the risks of parkinsonism from birth to a later age or death (first three lines of the
Discussion of findings
This study provides estimates of the risk of developing parkinsonism or PD while taking competing risks of death into account and it clearly illustrates the differences between lifetime risk and cumulative incidence. The difference between risk and cumulative incidence increased with age, reflecting the increasing risk of dying from other causes with age. After age 80 years, despite a sharp rise in the cumulative incidence of parkinsonism and PD, the risk increased less markedly because the
Acknowledgements
Dr. Elbaz completed this study while on leave from INSERM Unit 360, Recherches Épidémiologiques en Neurologie et Psychopathologie, Hôpital de la Salpêtrière, Paris, France. This investigation was financially supported by the NIH Grant NS33978, and was made possible by the Rochester Epidemiology Project (AR30582). We thank Rita Black, RN, for her assistance with medical records abstracting and Tonya Anderson and Elisa Underhill for typing the manuscript.
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