Objective: To describe the distribution of the age at onset in PD incidence studies and to compare this with the age of onset of published studies in PD.

Background: Most sources (e.g. textbooks, review articles, patient information) state that the mean age at onset in Parkinson’s disease (PD) is about 60. The only reliable way to identify the true age distribution in a population of PD is through population-based incidence studies, which aim to identify all new cases of PD in a defined population over a specific time period.

Methods: We performed a comprehensive systematic review to identify all incidence studies in PD. From identified studies, we extracted data relating to mean age at onset (or diagnosis) and age-specific incidence rates. We performed Der Simonian and Laird random-effects meta-analysis of mean age at inception (i.e. either onset or diagnosis). We also performed meta-analysis of age-specific incidence rates (in 10-year age bands) in studies published since 2000 and plotted a histogram to illustrate the average distribution of the age of incident PD. We subsequently documented the mean age at onset in all research studies in PD published over six months in Movement Disorders (July to September 2016), and compared this to the pooled mean age at inception from the identified incidence studies

Results: Twelve incidence studies reported data on the mean age at inception in PD. The pooled mean age was 69.3 (95% confidence interval 67.0–71.7) (figure 1) although major heterogeneity was present (I² = 96.8%). Some of the heterogeneity may be due to differences between age at onset and age at diagnosis. There was greatest heterogeneity in the oldest age stratum suggesting that some of the heterogeneity may be due to underascertainment in the elderly. The distribution of the age at inception in PD is displayed in figure 2. Of 41 studies published in Movement Disorders during the stated time period, 31 published the mean age at onset. The mean mean age at onset in these studies was 59.1 (median 58.9).

Conclusions: The mean age at onset in PD is nearly 70 which is both about ten years older than usually stated and about 10 years older than the mean age at onset in research participants. Many published studies have therefore used unrepresentative patient groups. This selection bias may have an important impact on the accuracy research findings as well as generalisability and further research should assess its influence.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/research-participants-are-not-representative-of-the-population-age-distribution-of-pd/