Time Trends in the Incidence of Parkinson Disease

Abstract

Importance: Changes over time in the incidence of parkinsonism and Parkinson disease (PD) remain uncertain.

Objective: To investigate secular trends (period effects) and birth cohort trends in the incidence of parkinsonism and PD over 30 years in a geographically defined American population.

Design, setting, and participants: We used the medical records-linkage system of the Rochester Epidemiology Project to identify incidence cases of PD and other types of parkinsonism in Olmsted County, Minnesota, from 1976 to 2005. All cases were classified by a movement disorder specialist using defined criteria through the review of the complete medical records within the system. The analyses for this study were conducted between May 2015 and January 2016.

Main outcomes and measures: Incidence rates of parkinsonism and PD over 30 years. We tested for secular trends (period effects) using negative binomial regression models and for birth cohort effects using age-period-cohort models.

Results: Of 906 patients with parkinsonism, 501 were men, and the median age at onset was 74 years (interquartile range, 66-81 years). Of the 464 patients with PD, 275 were men, and the median age at onset was 73 years (interquartile range, 64-80 years). The overall incidence rates increased significantly over 30 years in men for both parkinsonism (relative risk [RR], 1.17 per decade; 95% CI, 1.03-1.33) and PD (RR, 1.24 per decade; 95% CI, 1.08-1.43). These trends were driven primarily by the older age groups. In particular, for men 70 years or older, incidence rates increased for both parkinsonism (RR, 1.24 per decade; 95% CI, 1.07-1.44) and PD (RR, 1.35 per decade; 95% CI, 1.10-1.65). The secular trends were not significant for women overall or in age strata. We observed an increased risk for both men and women born in the 1920 cohort (1915-1924). However, this birth cohort effect was significant only for PD and only in men.

Conclusions and revelance: Our study suggests that the incidence of parkinsonism and PD may have increased between 1976 and 2005, particularly in men 70 years and older. These trends may be associated with the dramatic changes in smoking behavior that took place in the second half of the 20th century or with other lifestyle or environmental changes. However, the trends could be spurious and need to be confirmed in other populations.

Figure 1. Secular Trends in Incidence Rates (Period Effects)

Incidence rate curves for men and women estimated using single calendar year data points (directly standardized by age to the total 1990 US population) and negative binomial regression (top panels, parkinsonism overall; bottom panels, Parkinson’s disease). The relative risk (RR) refers to the average increase in incidence rate over 10 years.

Figure 2. Birth Cohort Trends in Incidence Rates

Birth cohort curves of age- and sex-specific incidence rates for parkinsonism overall (top panels) and Parkinson’s disease (bottom panels). The central year of each 10-year birth cohort served as the cohort label. Each birth cohort contributed three age-specific incidence rates that are shown with different colors and symbols.

Figure 3. Analyses Using Age-period-cohort Models

Birth cohort component of the age-period-cohort models for parkinsonism overall (top panels) and Parkinson’s disease (bottom panels) in men and women separately. The birth cohort effects were displayed relative to 1920 (median year of birth for all parkinsonism patients; circle with relative risk of 1.0) and fixing the period component to 1990 (mid-point of the study interval). For a given birth cohort year (x-axis), the figure shows the ratio of the incidence rate in that year compared with the incidence rate in the 1920 birth cohort (relative risk on the y-axis).