Prevalence and Characteristics of Periodic Limb Movements during Sleep in Korean Adult Patients with Restless Legs Syndrome

Study Objectives: The aim of this study was to investigate the prevalence and characteristics of periodic limb movements during sleep (PLMS) in Korean patients with restless legs syndrome (RLS). Methods: Unmedicated adult patients with idiopathic RLS (n = 354) who underwent polysomnography at three major sleep centers in tertiary hospitals were included. Characteristics of PLMS in RLS were analyzed using the time structure of polysomnographically recorded leg movements and periodicity indices (PIs). RLS severity and subjective sleep quality were assessed. Results: Out of 354 patients with idiopathic RLS (mean age: 52.9 +/- 12.0 years), 150 patients (42.3%) had RLS with a PLMS index greater than 15 events/h, and 204 (57.9%) had a PLMS index greater than 5 events/h. The distribution of inter-LM intervals was bimodal, and high PIs (0.86 +/- 0.10) were observed in patients with RLS and PLMS (PLMS index > 15 events/h). The PLMS index was positively correlated with age (r = 0.228; p < 0.001), the periodic limb movements in wakefulness index (r = 0.455, p < 0.001) and arousal index (r = 0.174, p = 0.014), but not with RLS severity and parameters of sleep quality. In multivariate analysis, age and male gender were independently associated with PLMS > 15 events/h. Conclusions: The prevalence of PLMS in Korean patients with RLS was lower than that observed in Western countries, but the characteristics of PLMS were not different. Ethnic differences and/or different genetic backgrounds may contribute to the varying prevalence of PLMS in RLS.