Has incidence of Parkinson's disease increased over past 30 years?

A previous study suggested smokers may have reduced risk of Parkinson disease (PD) and speculated the decline in smoking by men in the U.S. after a peak in the 1940s and 1950s could result in an increase in PD incidence decades later. That theory has not been tested empirically.

As a result, Walter A. Rocca, M.D., M.P.H., of the Mayo Clinic, Rochester, Minn., and coauthors studied time trends for parkinsonism and for PD in Olmsted County, Minn., from 1976 to 2005.

Parkinsonism was defined as the presence of at least two cardinal signs: rest tremor, bradykinesia, rigidity and impaired postural reflexes. PD was defined as parkinsonism with all three of the following features: no other cause, no documentation of unresponsiveness to levodopa, and no prominent or early signs of more extensive nervous system involvement.

The study included 906 patients with parkinsonism with a median age at onset of 74, of whom 501 were men. Of the 464 patients with PD with a median age of onset at 73, 275 were men.

Incidence rates of parkinsonism increased in men from 38.9 per 100,000 person-years between 1976 and 1985 to 55.9 between 1996 and 2005. Rates of PD increased in men from 18.2 between 1976 and 1985 to 30.4 between 1996 and 2005 and the increase was greater for men over 70 or older. No similar overall trends were seen for women, according to the results.

The authors note their trends should be interpreted with caution for a variety of reasons, including that they may be due to increased awareness of symptoms, improved access to care of patients, and better recognition by physicians.

The authors suggest the trends they report may suggest a possible association with a change in smoking behavior. The prevalence of smoking has declined over time. However, other important lifestyle and environmental changes also have taken place over the decades.

"Our study suggests that the incidence of parkinsonism and PD may have increased between 1976 and 2005, particularly in men 70 years old 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," the study concludes.

Editorial: Are We Ready for a Potential Increase in Parkinson Incidence?

"The epidemiologic observation that cigarette smoking is associated with lower PD risk is robust but the debate over whether the association is causal seems never to be resolved. Given the substantial adverse health effects of cigarette smoking and low PD incidence, it is almost impossible to directly examine this question in clinical studies. However, results of the Savica et al study and a similar previous analysis may offer indirect support for causality: the increase of PD incidence may follow decrease in cigarette smoking over the past 50 years, a trend that also affects men more than women," Honglei Chen, M.D., Ph.D., of the National Institute of Environmental Health Sciences, Triangle Park, N.C., writes in a related editorial.