Respiratory-related leg movements and periodic leg movements during sleep

Abstract

Introduction The aim of the study was to describe the time structure of leg movements (LM) in obstructive sleep apnea syndrome (OSAS), in order to add new knowledge to the understanding of their clinical significance. Materials and methods Eighty-four patients (16 females, 68 males, mean age 55.1 years, range 29–74) were recruited. All subjects underwent full-night polysomnography and the leg motor pattern was evaluated by means of advanced tools of analysis particularly able to detect and describe LM time structure (periodicity and distribution). In particular, respiratory-related LM (RRLM) were separated from those not related to respiratory events (NRLM). Results OSAS patients with RRLM had leg movement parameters generally higher subjects without RRLM; the effect was strong for the periodic LM during sleep (PLMS) index, in particular during NREM sleep. The NRLM intermovement interval distribution histogram of patients with RRLM showed a prominent first peak at 4 s, followed by another at approximately 24 s (corresponding to typical PLMS). In the same group, RRLM showed a single wide lower peak with a maximum at about 42 s. In patients without RRLM, NRLM were evident with a single peak at 2–4 s. Patients with RRLM showed a gradually decreasing number of NRLM, from the first to the last hours of sleep; this pattern was less clear for RRLM. A stepwise linear regression analysis showed that, even when controlling for RLS status and AHI, PLMS were highly significantly associated with RRLM. Conclusion This study shows that RRLM might be part of the true PLMS because they cluster clearly in the patients who also have typical PLMS not correlated with the respiratory events.