In this large cohort of men, we observed that men with RLS had a higher prevalence of PD than those without RLS, across all age groups. Compared to men without RLS, those who reported having RLS symptoms 15 or more times per month had approximately three-fold higher prevalence of PD. Strengths of the current study include a large sample size, which enabled us to obtain a relatively stable estimate for the associations, and use of standardized questionnaire to assess RLS. As we did not collect information on several RLS-like syndrome (e.g., peripheral neuropathy, leg cramps, positional discomfort, radiculopathy), some misclassification in RLS assessment is possible. However, results were similar when we included or excluded men with diabetes, the most common cause of peripheral neuropathy, in our analyses. Another limitation is that we included only men and therefore our results cannot be generalized to women. Further, because of the cross-sectional design of our study, we are not able to know whether RLS occured before onset of PD or vice versa.
Associations between RLS and PD have been noticed for long time; 17, 18
both conditions are associated with dopamine hypofunction in CNS. Our findings are consistent with the results of some previous epidemiological studies,5, 6, 19
but not others.7
In a sample of 125 PD patients in Singapore, Tan et al reported that none of them met IRLSSG diagnostic criteria of RLS.7
However, recently, Loo and Tan found a marginally significant higher prevalence of RLS among PD cases (n=400) than controls (3% vs. 0.5%; P=0.07) in Singapore.19
In a cross-sectional study by Ondo et al, 20.8% of 303 PD patients had RLS symptoms.20
In a study examining prevalence of PD among RLS patients,21
Walters et al. found that 4 out of 85 RLS cases (4.7%) had PD, compared to ~1% PD prevalence expected among the general population over age 60. A recent report showed that in a family with a high prevalence of RLS, two (6.7%) out of 30 family member with RLS also had PD.22
However, none of these three studies included control groups. Interestingly, a recent genome-wide association study found that MEIS1, a gene involved in embryonic development of substantia nigra, was associated with RLS risk.23
The relation between MEIS1 and PD risk has only been reported in one case-control study, and was not significant. 24
In conclusion, we found a concurrence between RLS and PD in men. Further prospective studies are warranted to clarify whether the presence of RLS precedes onset of classic motor symptom of PD; if so, screening for RLS could help to identify individuals at high risk for PD.