Multimorbidity and the risk of restless legs syndrome in 2 prospective cohort studies.

OBJECTIVE

Our aim was to evaluate the association between the cumulative effect of comorbidity and the risk of restless legs syndrome (RLS) in 2 population-based German cohort studies.

METHODS

The Dortmund Health Study (DHS) (n = 1,312; median follow-up time: 2.1 years) and the Study of Health in Pomerania (SHIP) (n = 4,308; median follow-up time: 5.0 years) were used for the analyses. RLS was assessed at baseline and follow-up according to the RLS minimal criteria. A comorbidity index was calculated as a sum of the following conditions: diabetes, hypertension, myocardial infarction, obesity, stroke, cancer, renal disease, anemia, depression, thyroid disease, and migraine. The relationship between comorbidity and incident RLS was analyzed with multivariate logistic regression models.

RESULTS

An increase in the number of comorbid conditions at baseline predicted prevalent RLS (DHS: trend odds ratio [OR] = 1.24, 95% confidence interval [CI] 0.99-1.56; SHIP: trend OR = 1.34, 95% CI 1.18-1.52) and incident RLS (DHS: trend OR = 1.32, 95% CI 1.04-1.68; SHIP: trend OR = 1.59, 95% CI 1.37-1.85) after adjustment for several covariates. The ORs for incident RLS associated with 3 or more comorbid diseases (DHS: OR = 2.51, 95% CI 1.18-5.34; SHIP: OR = 4.30, 95% CI 2.60-7.11) were higher than the ORs for any single disease.

CONCLUSIONS

Multimorbidity was a strong risk factor for RLS in these 2 population-based cohort studies. The results support the hypothesis that cumulative disease burden is more important than the presence of a specific single disease in the pathophysiology of RLS.