To what extent and why are COPD and Willis-Ekbom disease associated?

AIM: Willis-Ekbom disease (RLS/WED) is common in chronic obstructive pulmonary disease (COPD). Patients with RLS/WED have poorer quality of sleep and more fatigue and depressive symptoms. The prevalence of RLS/WED in patients with COPD has been reported to vary between 29.1 and 36.8 %. However, during exacerbation, the prevalence can increase up to 54 %. These rates are higher than those seen in general population. We have not enough knowledge regarding the association between RLS and COPD. In this study, we aimed to determine the frequency of RLS in patients with stable COPD without comorbid conditions. In addition, we also aimed to determine possible related causative factors.
METHOD: We included 80 COPD patients without comorbid conditions who presented to our outpatient clinic between April 2013 and September 2013 for RLS/WED evaluation. Three cases that have polyneuropathy and one case that refused undergoing electromyography (EMG) examination were excluded from the study. Demographic data, P-A chest X-rays, pulmonary function tests (PFT), biochemical parameters (including hemogram), and dyspnea scales were evaluated for each patient. In addition, the RLS/WED rating scale and Epworth Sleep Scale (ESS) were applied. Further, each patient diagnosed with RLS/WED underwent a detailed neurological examination (performed by a neurologist) and an EMG examination to rule out polyneuropathy.
RESULTS: Out of 76 COPD cases included in our study, 26.3 % (n = 20) were diagnosed with RLS/WED (mean age 60.4 ± 7.5 years, 20 males). The cases with RLS/WED had significantly lower body mass index (BMI) than cases without RLS/WED (p = 0.009). There were no significant differences between cases with and without RLS/WED with respect to PFT, dyspnea scales, and arterial blood gas values. However, ESS was significantly different (p = 0.016). There were no significant differences in RLS/WED scores and mean hs-CRP levels between COPD stages (p = 0.424; p = 0.518, respectively), while ESS was significantly different (p = 0.016). ESS was significantly higher in stage B COPD than in stages A and D (p = 0.005, p = 0.008, respectively). Based on our model, we found that exacerbations and iron binding capacity (UIBC) were predictive factors for RLS/WED (p < 0.100)
CONCLUSION: RLS/WED is a common disease in cases with stable COPD. Despite our hypothesis suggesting that the prevalence of RLS/WED in COPD is related with systemic inflammation, we did not find a significant association between hs-CRP and COPD cases with RLS/WED. However, we did find that UIBC is a predictive factor for the development of RLS/WED. Nonetheless, further studies are needed to understand the relationships between UIBC, low BMI, and the development of RLS/WED in COPD.