Parkinson's Disease Incidence May Be Growing

Findings from a study published in JAMA Neurology suggest an increase in the incidence of Parkinson’s disease and parkinsonism over the past 30 years.

In the study researchers studied time trends for parkinsonism and Parkinson’s disease in Olmsted County, Minnesota, from 1976 to 2005. Parkinsonism was defined as the presence of at least 2 of the signs: bradykinesia, rest tremor, and rigidity and impaired postural reflexes; Parkinson’s as parkinsonism with all 3 other factors: no prominent or early signs of more extensive nervous system involvement, no other cause, no documentation of unresponsiveness to levodopa.

For the study, researchers enrolled 906 patients with parkinsonism. The median age of onset was 74-years-old, 501 of whom were men. For Parkinson’s disease, there were 464 patients with a median onset age of 73-years-old, 275 whom were men.

The results of the study showed that the 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. For Parkinson’s disease, the rates increased from 18.2 between 1976 and 1985 to 30.4 between 1996 and 2005.

The increase was found to be greater for men who were 70-years-old and above.

“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,” the authors wrote. “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.”

Although the trends suggest a possible association with a change in smoke behavior since the prevalence of smoking has declined over time, there are other lifestyle and environmental changes that have also taken place that could have an effect.

The authors noted that the trends they found should be interpreted with caution since there could be a variety of reasons for these trends such as increased awareness of symptoms, better recognition by physicians, and an improvement in patient access to care.

“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,” wrote Honglei Chen, MD, PhD, in a related editorial. “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.”