In recent years, investigators have learned much about the causes of Parkinson disease (PD), and greater efforts have been made to develop medications and treatments to manage PD. “Time trends of a given disease are an important way to monitor changes in lifestyle and the effectiveness of public health and medical practice,” explains Walter A. Rocca, MD, MPH.
Recent studies have suggested that there has been a decline in the risk of people developing dementia and stroke but an increased risk for developing PD and amyotrophic lateral sclerosis. “These opposing trends may suggest that better lifestyle and improved medical care for conditions like hypertension and hyperlipidemia have prompted a decline in neurovascular lesions and mechanisms,” Dr. Rocca says. “However, the neurodegenerative lesions and mechanisms—such as plaques, tangles, Lewy bodies, and brain atrophy—may be increasing at the same time.”
Dr. Rocca also notes that clinicians are beginning to see some important differences in risks for neurologic disease between men and women. “There appears to be a more pronounced decline in dementia risk among women, whereas increases in PD risk are more pronounced in men,” says Dr. Rocca. “Sex and gender factors are interacting with historical changes in environment and lifestyle over time.”
Examining Long-Term Data
For a study published in JAMA Neurology, Dr. Rocca and colleagues examined time trends for parkinsonism overall and for PD over a period of 30 years using data from a well-defined United States population. The authors used the medical records–linkage system of the Rochester Epidemiology Project to identify incidence cases of PD and other types of parkinsonism in Olmsted County from 1976 to 2005. “This system enabled us to learn more about the long-term general trends in neurologic diseases because it had records in place for 50 years,” adds Dr. Rocca.
Of the 906 patients with parkinsonism involved in the study, more than half were men (501 patients) and the median age of onset was 74 years of age. There were 464 patients with PD, 275 of which were men, and the median age of onset for PD was 73 years. “We were surprised to find an increase in the risk of PD over 30 years,” Dr. Rocca says. “The greater increase in incidence among men aged 70 and older, when compared with younger men, may be a birth cohort effect. Men born between 1915 and 1924 had the highest risk of PD, but the risk was lower in subsequent decades. Men born between 1915 and 1924 were approximately 60 years old between 1976 and 1985, 70 years old between 1986 and 1995, and 80 years old between 1996 and 2005.”
Dr. Rocca says the observed birth cohort effect may suggest some intrauterine events, such as poor diet or some type of infection experienced by the mother. “On the other hand, the birth cohort may simply indicate that men were within a certain age range during some important events of last century,” he says. “These include World War II, the introduction of chemical toxins in agriculture, the introduction of certain drugs on the market, and changes in smoking incidence, diet, and lifestyle.”
The study group noted there was an observed increased risk for PD among both men and women born in the 1920s cohort (1915-1924). However, this birth cohort effect was significant only for PD and only in men. The incidence rates for parkinsonism of all types and for PD were higher in men than in women across all 3 decades analyzed in the investigation.
Considering the Implications
If the increasing trend of PD and parkinsonism is confirmed in other populations in the U.S. and internationally, currently available projections for the coming 20 to 30 years will need to be modified, Dr. Rocca says. “We observed an approximate 60% increase in the incidence of PD in men and women combined over 30 years,” he says. “The increase was approximately 120% for men and women combined who were aged 70 or older. A rising number of people affected by PD will cause changes in the neurological care needs and will likely increase the cost of care for these patients.”
It is important to confirm the increasing trend of PD in other populations, according to Dr. Rocca. “If trends are confirmed, we then need to examine possible ecological links with time trends in agricultural chemicals, infectious diseases, diet, and lifestyle. If PD is connected—to some extent—to events taking place during intrauterine life or early development, it’s also important to conduct research to explore this hypothesis.”
Dr. Rocca notes that he and his colleagues are currently publishing a new article on time trends for drug-induced parkinsonism. “We have observed an opposing trend in this research,” he says. “There appears to have been a decline in the incidence rate over the same 30 years in which the rate of PD increased. We hope to learn more about these trends in the future.”
Walter A. Rocca, MD, MPH, has indicated to Physician’s Weekly that he has or has had no financial interests to report.
Readings & Resources (click to view)
Savica R, Grossardt BR, Bower JH, Ahlskog E, Rocca WA. Time trends in the incidence of Parkinson disease. JAMA Neurol. 2016;73:981-989. Available at: http://archneur.jamanetwork.com/article.aspx?articleid=2529538.
Savica R, Grossardt BR, Bower JH, Ahlskog JE, Rocca WA. Risk factors for Parkinson’s disease may differ in men and women: an exploratory study. Horm Behav. 2013;63:308-314.
Morozova N, O’Reilly EJ, Ascherio A. Variations in gender ratios support the connection between smoking and Parkinson’s disease. Mov Disord. 2008;23:1414-1419.
RoccaWA, Bower JH, McDonnell SK, Peterson BJ, Maraganore DM. Time trends in the incidence of parkinsonism in Olmsted County, Minnesota. Neurology. 2001;57:462-467.
Dorsey ER, Constantinescu R, Thompson JP, et al. Projected number of people with Parkinson disease in the most populous nations, 2005 through 2030. Neurology. 2007;68:384-386.