Variability of Periodic Leg Movements in Various Sleep Disorders: Implications for Clinical and Pathophysiologic Studies

STUDY OBJECTIVESPeriodic leg movements in sleep (PLMS) are a frequent phenomenon in various sleep disorders. The pathophysiology of PLMS is still not understood, but recent studies indicate a hypoactivity of the dopaminergic system in subjects with PLMS. In the present study, we investigated the intrasubject variance of PLMS from one night to the other because a fluctuation in the number of PLMS may influence the outcome of pharmacologic and pathophysiologic studies.DESIGNRetrospective observational study.SETTINGData collection occurred in the sleep disorders unit.PATIENTSSleep electroencephalogram and PLMS data of 115 patients with PLMS monitoring over 2 consecutive nights were evaluated retrospectively. Patients were grouped into the following diagnostic categories: restless legs syndrome, insomnia secondary to a psychiatric disorder, primary insomnia, sleep apnea syndrome, and narcolepsy or idiopathic hypersomnia.INTERVENTIONSN/A.RESULTSIn 27% of the entire patient population, we found a considerable variability of the PLMS index (difference between nights > 10/hour) and, in 19% of patients, variability of the PLMS arousal index (difference between nights > 5/hour) across the 2 investigated nights. The intraindividual variance occurred most frequently and to the highest extent in patients with RLS.CONCLUSIONSThe variability of PLMS indexes should considered if the PLMS recording is performed in support of the clinical diagnosis or in the interpretation of studies investigating drug efficacy. Furthermore, the variability of PLMS may be an indicator of an instability of the dopaminergic system that should be taken into account in studies investigating central nervous system dopaminergic activity.