Ethnic differences in periodic limb movements during sleep in patients with restless legs syndrome: a preliminary cross-sectional study of Austrian and Japanese clinical population

Periodic limb movements during sleep (PLMS) are identified as a common finding in patients with restless legs syndrome (RLS). Although PLMS are observed in more than 80% of RLS patients in Western countries, little is known about Asian RLS patients and no data are available about Japanese patients. This cross-sectional study aimed to investigate ethnic differences in clinical information and polysomnographic variables including PLMS between Austrian and Japanese RLS patient undergoing nocturnal polysomnography (n-PSG). One hundred Austrian and 139 Japanese consecutive patients diagnosed with RLS who underwent n-PSG were included [Austrian 54.5 ± 13.6 years, 40 females (40%); Japanese 50.2 ± 18.9 years, 88 females (63.3%)]. Medical records and n-PSG data were reviewed retrospectively. Epidemiological, clinical and n-PSG variables were compared between the two groups. Rate of patients with PLMS ≥ 5/h and those with PLMS ≥ 15/h were higher in Austrian than in Japanese RLS patients (80.0 vs. 56.1%, P < 0.001; 55.0 vs. 41.7%, P = 0.043). Accordingly, Japanese RLS patients showed lower PLMS index than Austrian patients (21.3 vs. 33.6/h, P = 0.008). Japanese RLS patients showed higher female predominance, lower BMI, lower systolic/diastolic blood pressure, lower ferritin level and higher International restless legs syndrome severity scale than Austrian patients. None of these variables were associated with PLMS in both groups. Japanese RLS patients showed significantly lower comorbidity rate and lower indices of PLMS compared to Austrian RLS patients. This cross-sectional study on ethnic differences in PLMS in patients with RLS may provide a bridge to a future genetic comparative study between European and Asian RLS patients.