Different sleep characteristics in restless legs syndrome and periodic limb movement disorder

Objective: Periodic limb movements in sleep (PLMS) may or may not be associated with restless legs syndrome (RLS). The number of PLMS is commonly used to assess the clinical severity and sleep quality of patients with RLS. It is still unclear whether the sleep disorder of periodic limb movement disorder (PLMD) is different from the sleep disorder in RLS. Methods: We compared the polysomnograms (PSGs) of 27 prospectively recruited RLS patients and 26 retrospectively recruited age- and sex-matched PLMD patients without RLS symptoms. Results: The PLM index and the index of arousal-associated PLMS (PLMAI) were significantly higher in PLMD, whereas the index of EEG arousals not associated with any sleep-related event was significantly higher in RLS. In PLMD patients, the PLMI correlated negatively with the percentage of PLMS associated with an arousal, whereas this correlation was positive in RLS patients. Further, RLS patients spent significantly more time in wake-after-sleep onset, had more rapid eye movement sleep (REM) and less sleep stage I. Conclusions: We conclude that the sleep disorder in RLS differs from that in PLMD. Spontaneous, not PLM associated EEG arousals should be included in the assessment of the sleep structure of patients with RLS, particularly in studies concerned with drug-efficacy.