Conversion Rate of Essential Tremor to Essential Tremor Parkinson Disease
Data From a Prospective Longitudinal Study
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Abstract
Background and Objectives There has been a long-standing dialog as to whether essential tremor (ET) increases the risk of developing Parkinson disease (PD). While there are relevant cross-sectional data, there are almost no longitudinal prospective data. We quantified the conversion rate from ET to ETPD in a prospective longitudinal cohort study of patients with ET. We compared the observed rate with that reported in the epidemiologic literature.
Methods We enrolled patients with ET in a prospective, longitudinal study. A senior movement disorders neurologist evaluated standardized neurologic examinations every 18 months.
Results One hundred ninety-three patients with ET (mean age = 78.1 ± 9.6 years, range = 55–96) had a mean follow-up duration of 4.1 years. Seven (3.6%) converted from ET to ETPD. The incidence of PD among patients with ET was 7/792.9 person-years (py; i.e., 882.8/100,000 py). A meta-analysis of the incidence (per 100,000 py) of PD in 14 studies from 13 countries across 4 continents reported an incidence of PD = 61.21 (men, 40 years or older) and 37.55 (women, 40 years or older). The incidence/100,000 py in men peaked in the 80- to 89-year-old age group (258.47) and in women in the 80- to 89-year-old age group (103.48 py). The abovementioned published values are 3.4–23.5 times lower than the value we observed for ET.
Discussion The incidence of PD in an ET cohort is substantially higher than that reported in historical population-based control groups across numerous countries. Additional prospective longitudinal data are needed to further explore this association.
Footnotes
Funding information and disclosures are provided at the end of the article. Full disclosure form information provided by the authors is available with the full text of this article at Neurology.org/cp.
Submitted and externally peer reviewed. The handling editor was Associate Editor John P. Ney, MD, MPH.
- Received November 21, 2022.
- Accepted March 2, 2023.
- © 2023 American Academy of Neurology
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