Background: A longstanding literature suggests an association between essential tremor (ET) and Parkinson’s disease (PD). However, the risk of incident PD has not been quantified in cases of ET compared with controls.
Objective: To estimate the risk of incident PD in a population based cohort study of 3813 older people (including ET cases and controls) in central Spain.
Results: After a median of 3.3 years, 12 (5.8%) of 207 ET cases developed parkinsonism compared with 56 (1.6%) of 3606 controls (adjusted relative risk (RR) 3.47, 95% CI 1.82 to 6.59; p<0.001). Six (3.0%) of 201 ET cases developed incident PD versus 24 (0.7%) of 3574 controls (adjusted RR 4.27, 95% CI 1.72 to 10.61; p = 0.002).
Conclusions: Patients with ET were four times more likely than controls to develop incident PD during prospective follow-up. These data confirm and begin to quantify the link between these two diseases.
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Competing interests: None.
Funding: The NEDICES was supported by the Spanish Health Research Agency (FIS 93/0773 and 96/1993) and the Spanish Office of Science and Technology. EDL is supported by NIH R01 NS042859 and R01 NS039422 from the National Institutes of Health, Bethesda, Maryland, USA.
Ethics approval: Ethics approval was obtained.
Contributors: EDL and JB-L, developed the concept of the article, drafted the paper and conducted the statistical analysis. All authors were involved in revising the article for intellectual content.
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