Incidence of Parkinson’s in US More Than Previously Estimated

Updated data should help guide treatment research and healthcare policies

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Nearly 90,000 people, 65 or older, are diagnosed with Parkinson’s disease every year in the U.S., representing an increase of about 50% relative to previous estimates of the disease’s incidence, a study showed.

“These updated estimates of incidence are necessary for understanding disease risk, planning health care delivery, and addressing care disparities,” James Beck, PhD, one of the study’s authors and the chief scientific officer at the Parkinson’s Foundation, said in a press release.

“Knowing this information will allow us to better serve people with Parkinson’s and their families and plan for adequate health care services in the future,” Beck added.

Brian Fiske, PhD, another of the study’s authors and the chief scientific officer at The Michael J. Fox Foundation for Parkinson’s Research, said that “the growth in those diagnosed and living with PD [Parkinson’s disease] underscores the need to invest in more research toward better treatments, a cure, and one day, prevention.”

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“It’s also a clear call to lawmakers to implement policies that will lessen the burden of Parkinson’s disease on American families and programs like Medicare and Social Security,” Fiske said.

The study, “Incidence of Parkinson disease in North America,” was published in npj Parkinson’s Disease. It was supported by both the Parkinson’s Foundation and The Michael J. Fox Foundation, as well as the Institute for Clinical Evaluative Sciences.

Previous estimates of the incidence of Parkinson’s in North America have put the number at around 40,000 to 60,000 cases diagnosed per year. However, these studies generally have been extrapolating from relatively limited datasets.

To gain a better understanding of the disease’s incidence for a given year, researchers conducted an analysis of five large healthcare datasets: four from the U.S. and one from Canada.

The largest, containing data for nearly 7 million people, was derived from Medicare, the public program that provides health insurance for people 65 or older in the U.S.

“We estimated the incidence of Parkinson disease simultaneously across five epidemiological datasets using commonly applied diagnosis and case ascertainment methods applied to 2012 data,” the researchers wrote. The year 2012 was chosen based on data availability.

Results showed that age- and sex-adjusted incidence rates varied between the datasets. The team noted that this was partly because the datasets used different clinical criteria to determine whether a person would be diagnosed formally as having Parkinson’s. Datasets with stricter requirements generally had lower estimates.

Among people ages 45 or older, the incidence of Parkinson’s was 47 to 77 per 100,000 persons, totaling 60,000 to 95,000 new cases per year in North America. Based on the data, the researchers proposed a “working estimate” incident rate of 62 people, ages 45 and older, per 100,000 person-years.

Person-years is a measure of the number of people participating in the study and the amount of time they were followed. For example, 100,000 person-years refers to data gathered from 100,000 patients who were followed for one year.

Based on available population data, that works out to a total of about 77,000 newly diagnosed cases in 2012, and about 86,000 cases in 2020.

Age matters

As expected for an aging-related disease, Parkinson’s incidence was even higher among people 65 or older, ranging from 108 to 212 per 100,000 persons in 2012. When looking at Medicare data alone, the total number of older people newly diagnosed with the disease in the U.S. would be nearly 90,000 for that same year.

Further analyses showed that “the primary risk factor for PD is age, and within all [datasets], we found that PD incidence increased into the 7th decade,” the researchers wrote.

In addition to age, the disease incidence varied by sex. Across age groups, rates were significantly higher among men than women — by more than twofold in some comparisons.

“The male: female ratio for incident PD increased with age in all epidemiological [datasets] in our study, consistent with the previous data that supports the hypothesis that biological sex is an intrinsic risk factor,” the researchers wrote.

The ‘Parkinson’s belt’

Based on Medicare data, Parkinson’s incidence also varied geographically across the U.S. The highest incidences were seen in the “Rust Belt” — regions of the Midwest, South, and Appalachia with a history of heavy industry manufacturing — and in southern California, southeastern Texas, and Florida.

This so-called “Parkinson’s belt,” was “originally described using PD incidence estimates from 2005,” and “was still present in 2012,” the team wrote.

“The persistence of the Parkinson’s disease belt in the U.S. might be due to population, health care or environmental factors,” said Allison Willis, MD, the study’s first author and associate professor of neurology in the Perelman School of Medicine at the University of Pennsylvania.

Overall, “PD incidence estimates varied across our data sources, in part due to case ascertainment and diagnosis methods, but also possibly due to the influence of population factors (prevalence of genetic risk factors or protective markers) and geographic location (exposure to environmental toxins),” the researchers wrote.

“Understanding the source of these variations will be important for health care policy, research and care planning,” Willis added.

The researchers stressed that these estimates are only approximations, and that the study’s retrospective nature comes with some limitations.

Moreover, incidence estimates for the current year may be even higher due to increases in risk factors or greater recognition of Parkinson’s symptoms, while a potentially reduced exposure to environmental toxicants or fewer diagnoses “due to COVID-related changes in health care-seeking behavior” may negatively affect them, the team wrote.

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