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Incidence and remaining lifetime risk of Parkinson disease in advanced age

From the Divisions of Aging (J.A.D., J.M.G., T.K.) and Preventive Medicine (J.M.G., T.K.), Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA; Department of Neurology and Psychiatry (G.L.), School of Medicine, University of Bari, Italy; Department of Epidemiology (T.K.), Harvard School of Public Health, Boston, MA; and Massachusetts Veterans Epidemiology Research Information Center (J.M.G.), VA Boston Healthcare System, Boston, MA.

Address correspondence and reprint request to Dr. Jane A. Driver, Division of Aging, Brigham and Women's Hospital, 1620 Tremont St., Boston, MA 02120 jdriver{at}partners.org

Objective: To estimate the incidence and lifetime risk (LTR) of Parkinson disease (PD) in a large cohort of men.

Background: Age is the strongest risk factor for PD, but whether its incidence continues to increase after age 80 years remains unclear.

Methods: Prospective cohort of 21,970 US male physicians aged 40–84 years at baseline who did not report PD before study entry. Participants self-reported PD on yearly follow-up questionnaires, and all deaths were confirmed. We calculated incidence rates and cumulative incidence using a modified Kaplan–Meier analysis. LTR was estimated by adjusting cumulative incidence for competing risks of death.

Results: Five hundred sixty-three cases of PD were identified over 23 years of follow-up. The crude incidence rate of PD was 121 cases/100,000 person-years. Age-specific incidence rates increased sharply beginning at age 60 years, peaked in those aged 85–89 years, and declined beginning at age 90 years. Cumulative incidence substantially overestimated the long-term risk of PD, particularly in those aged 80 years and older. Cumulative incidence was 9.9% (95% confidence interval [CI] 8.48%–11.30%) from ages 45 to 100 years, whereas LTR for the same period was 6.7% (95% CI 6.01%–7.43%). The incidence and LTR of PD decreased with increasing exposure to smoking.

Conclusions: Our study provides evidence that the incidence of Parkinson disease (PD) in men increases through age 89 years. Whether the subsequent decline represents a true decrease in risk remains to be established. A history of smoking substantially decreased the incidence and lifetime risk of PD. Incidence studies that do not adjust for competing risks of death may overestimate the true risk of PD in the elderly.

Abbreviations: AD = Alzheimer disease; CI = confidence interval; LTR = lifetime risk; PD = Parkinson disease; PHS = Physicians' Health Study.

The Physicians' Health Study is supported by grants CA-34944, CA-40360, and CA-097193 from the National Cancer Institute and grants HL-26490 and HL-34595 from the National Heart, Lung, and Blood Institute, Bethesda, MD. J.A.D. is supported by a grant from the Parkinson's Disease Foundation.

Disclosure: Author disclosures are provided at the end of the article.

Received July 14, 2008. Accepted in final form October 24, 2008.

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