A Rising Tide of Parkinson’s?

Results of a 30-year study suggest that Parkinson’s disease (PD) and related disorders are on the rise. Scientists led by Walter Rocca of the Mayo Clinic in Rochester, Minnesota, report in the June 20 JAMA Neurology that the number of new cases of parkinsonism has jumped every 10 years since 1976, particularly in men older than 70. This finding is in stark contrast to a measurable decrease in Alzheimer’s disease in Europe and the United States, which researchers attribute to healthier lifestyles of late (May 2013 news). “To our knowledge, [this] study is the first to examine long-term trends in PD incidence,” wrote Honglei Chen, National Institute of Environmental Health Sciences, North Carolina, in an accompanying editorial. If PD incidence has been growing at the rates they propose, it could present an enormous challenge to health care systems, he added.

Past studies that have looked at changes in PD incidence suggest that new cases have occurred at a relatively stable or even slightly declining rate (see Horsfall et al., 2013; Akushevich et al., 2013; Liu et al., 2016). However, many of these studies span a decade or less. In the new study, first author Rodolfo Savica wanted to use the rich data set available in the Rochester Epidemiology Project to look over a longer time frame. This population-based study, funded by the National Institute on Aging and the Mayo Clinic, tracks the medical records of almost all people who have lived in Olmstead County, Minnesota, since 1966.

Savica and colleagues scanned the database of records collected between 1976 and 2005 for those that contained diagnostic codes related to parkinsonism. Two movement disorders specialists then looked in detail at the 906 identified cases and diagnosed the type of movement disorder and when it developed. A disorder was labeled parkinsonism if a person had two of four cardinal signs: resting tremor, bradykinesia, rigidity, or impaired postural reflexes. Parkinson's disease was diagnosed if these symptoms had no other cause such as stroke or head injury, responded to levodopa, and didn’t appear to affect the wider nervous system.

The researchers found that for each consecutive 10-year block since 1976, the number of new cases of parkinsonism in men rose by 17 percent, while PD jumped by 24 percent. These differences were mainly driven by those over the age of 70, who experienced a 24 percent increase for parkinsonism, and a 35 percent hike for PD. For women, incidence appeared relatively stable over the time period. When the researchers analyzed disease incidence by birth year, men born between 1915 and 1924 were most likely to have the disease.

What could explain the trend? The authors note that if it were due to improvements in diagnosis, the same increases should apply to the women in the study. They suggest instead that the decline in smoking over the past 60 years could be responsible. Previous epidemiological studies have reported that cigarette smoking may prevent PD, but that has been controversial, not least because of the myriad reasons smoking is unhealthy (Ritz et al., 2014; Thacker et al., 2007; Morozova et al., 2008; Mar 2004 news). In the United States, smoking has been on the decline since its peak in the 1950s, especially in men, and could explain the increase in Parkinson’s, the authors wrote.

However, Chen noted that the authors had no data on smoking behavior or other possible risk factors for PD, and hence couldn’t analyze possible reasons. He also cautioned that these results come from a single county of mainly white people, so scientists should look for patterns in other populations.  The authors agreed that the results need to be confirmed in other cohorts.—Gwyneth Dickey Zakaib

Comments

  1. What about the incidence of pesticide utilization? PD incidence is increased in farmers. It would be interesting to have information about the possible exposure to environmental factors, profession, etc., of the patients involved.

    Somebody born between 1915 and 1924 might have been working in a farm, or working with loads of fruits and vegetables sprayed with pesticides, in the 1950s, when DDT and other pesticides (even more harmful than the current ones) were used in huge quantities and without precaution.

    References:

    Moisan F, Spinosi J, Dupupet JL, Delabre L, Mazurie JL, Goldberg M, Imbernon E, Tzourio C, Elbaz A. The relation between type of farming and prevalence of Parkinson's disease among agricultural workers in five French districts. Mov Disord. 2011 Feb 1;26(2):271-9. Epub 2010 Dec 13 PubMed.

    View all comments by Meduri Geri

  2. We agree that new data should be collected about occupational exposures of the patients with incident Parkinson’ disease (PD) in our population. The study could be designed as a case-control study comparing patients with PD to age and sex-matched controls free of PD. We conducted a similar case-control study in the patients who developed PD in Olmsted County, Minnesota, in the time period 1976-1995, and we found a significant association with pesticide use in men (Frigerio et al., 2006). On the other hand, farming in general was not found to be significantly associated with the risk of PD in Olmsted County in that time period (Frigerio et al., 2005).

    We hope to be able to obtain funding for a similar study for the patients with onset in the 1996-2010 time interval.

    References:

    Frigerio R, Sanft KR, Grossardt BR, Peterson BJ, Elbaz A, Bower JH, Ahlskog JE, de Andrade M, Maraganore DM, Rocca WA. Chemical exposures and Parkinson's disease: a population-based case-control study. Mov Disord. 2006 Oct;21(10):1688-92. PubMed.

    Frigerio R, Elbaz A, Sanft KR, Peterson BJ, Bower JH, Ahlskog JE, Grossardt BR, de Andrade M, Maraganore DM, Rocca WA. Education and occupations preceding Parkinson disease: a population-based case-control study. Neurology. 2005 Nov 22;65(10):1575-83. PubMed.

    View all comments by Walter A. Rocca

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References

News Citations

  1. Dementia Incidence Said to Drop as Public Health Improves
  2. Smoking Debate Still Smolders

Paper Citations

  1. Horsfall L, Petersen I, Walters K, Schrag A. Time trends in incidence of Parkinson's disease diagnosis in UK primary care. J Neurol. 2013 May;260(5):1351-7. PubMed.
  3. Liu WM, Wu RM, Lin JW, Liu YC, Chang CH, Lin CH. Time trends in the prevalence and incidence of Parkinson's disease in Taiwan: A nationwide, population-based study. J Formos Med Assoc. 2016 Jul;115(7):531-8. Epub 2015 Jun 27 PubMed.
  4. Ritz B, Lee PC, Lassen CF, Arah OA. Parkinson disease and smoking revisited: ease of quitting is an early sign of the disease. Neurology. 2014 Oct 14;83(16):1396-402. Epub 2014 Sep 12 PubMed.
  5. Thacker EL, O'Reilly EJ, Weisskopf MG, Chen H, Schwarzschild MA, McCullough ML, Calle EE, Thun MJ, Ascherio A. Temporal relationship between cigarette smoking and risk of Parkinson disease. Neurology. 2007 Mar 6;68(10):764-8. PubMed.
  6. Morozova N, O'Reilly EJ, Ascherio A. Variations in gender ratios support the connection between smoking and Parkinson's disease. Mov Disord. 2008 Jul 30;23(10):1414-9. PubMed.

External Citations

  1. Rochester Epidemiology Project 

Further Reading

Primary Papers

  1. Savica R, Grossardt BR, Bower JH, Ahlskog JE, Rocca WA. Time Trends in the Incidence of Parkinson Disease. JAMA Neurol. 2016 Jun 20; PubMed.

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