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The incidence of both parkinsonism and Parkinson disease (PD) appears to have increased from 1976 to 2005, particularly in men 70 years and older, a population-based study in Minnesota indicated.

The overall incidence rates increased significantly over 30 years in men for both parkinsonism (relative risk 1.17 per decade; 95% CI 1.03-1.33) and PD (RR 1.24 per decade; 95% CI 1.08-1.43), , of the Mayo Clinic, Rochester, Minn., and colleagues reported online in , using data on residents of Olmsted County, Minn., collected in a .

For men 70 years or older, incidence rates were the highest 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 study showed.

In addition, when 10-year birth cohorts were compared, an increased risk of Parkinson disease was observed in both men and women born in the 1920 (1915-1924) cohort. This finding was only significant in men, the researchers noted.

"If these trends are confirmed in other populations, they may be associated with the dramatic changes in smoking behavior during the last 50 years or with other lifestyle or environmental changes," they said.

These findings contradict several other studies reporting a stable or slightly decreased PD incidence over the years, Rocca and colleagues noted. "Our study provides evidence contrary to and one Canadian study that showed no trend and particularly contrary to suggesting a possible decline in the occurrence of PD over time. A study using Swiss mortality data suggested a possible , with higher risk for cohorts born before the 1920s."

In an accompanying editorial, , of the National Institute of Environmental Health Sciences at Research Triangle Park, NC, said that if these results are confirmed in other studies, they could have "important" implications for public health. It has been estimated that , based on its incidence in 15 countries 10 years ago, will double by 2030, climbing to 9 million, he pointed out.

"If, indeed, PD incidence has been increasing at the rates suggested [by this study] we would have to revise this estimate to an even larger number, presenting an enormous challenge to our health care system. Effective planning for this possibility will therefore be needed."

The Parkinson's Disease Foundation (PDF) views all current estimates of the prevalence of the disease "as likely inaccurate" -- those in the new Mayo study as well as previous ones, said , vice president of scientific affairs. He noted that they have been drawn from samples that fail to reflect the nation's full geographic and racial/ethnic diversity. The Olmsted County population, for example, is nearly 100% white and un-urbanized.

Beck said that PDF is using a diverse group of datasets to improve the accuracy of these estimates. "The answers will be the impetus to remind government, industry, and science of the urgency to better treat and end this disease."

On another front, Chen said the Mayo study moves researchers one step closer to closing the gap, albeit indirectly, on a between cigarette smoking and PD incidence. "The increase of PD incidence may follow decrease in , a trend that also affects men more than women," he noted.

The observation that PD incidence was higher for individuals born around the time of the 1918 influenza epidemic also points to the possible role of in risk for PD or parkinsonism late in life, he said. "The study attests to the importance of understanding fundamental epidemiology of neurodegenerative diseases and highlights the unique contributions that are possible by well-designed analyses of high-quality, longitudinal electronic medical records," Chen wrote.

A total of 906 patients with parkinsonism were identified. The median age at onset was 74 years and 501 were male. Of this group, 275 of 464 patients with PD were male with a median age at onset of 73 years.

"These trends were driven primarily by the older age groups," the researchers said. "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."

Limitations of the study included a small, all-white sample size without analysis of multiple system atrophy. Changes in clinical practice and diagnostic criteria in the intervening years may also have had an impact on results, the study authors noted.