Night-to-night variability in periodic leg movements in patients with restless legs syndrome

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Background and purpose Although a night-to-night variability in periodic leg movements (PLM) occurrence has been described in patients with primary PLM disorder and sleep apnea syndrome, no study has apparently considered the inter-night effect on PLM index during wakefulness and sleep in patients with Restless Legs Syndrome (RLS). Moreover, no study has examined the night-to-night variability in PLM index according to sleep stage and time of night. We therefore examined changes in PLM index during wakefulness and sleep during two consecutive nights in a group of untreated RLS patients. Patients and methods Twenty-eight drug-free RLS patients, aged 53.4±2.3 yr, with a mean International Restless Legs Syndrome Study Group (IRLSSG) severity score of 20.2±1.6, were studied during two consecutive nights. PLM duration and interval, PLM index during wakefulness (PLMWI), during total sleep time (PLMSI), as well as during each sleep stage were measured. Analysis was also extended to examine PLM occurrence during sleep cycles. Results In the group of patients as a whole, the PLMW and PLMS index, duration and interval did not show significant difference between nights, these measures being consistently similar for both nights. Comparison of PLMS index between different sleep stages did not reveal inter-night differences. Nocturnal variation in PLM number, duration and interval for total recording time and sleep period revealed a progressive decline across the night for PLM index ( P≤0.0001) but no interaction, the changes being similar in first and second nights. However, a large intra-individual variability was present with a correlation coefficient between nights of 0.60 for the PLMWI ( P=0.001) and 0.54 ( P=0.003) for the PLMSI. The individual inter-night changes in PLM index were independent of age, IRLSSG severity score, duration of the disease and changes in sleep parameters. Conclusions This study shows that the index and the nocturnal pattern of PLM occurrence are highly reliable across nights in RLS patients, suggesting that a single-night study may be sufficiently sensitive to confirm diagnosis and associated sleep disturbances in these patients. However, an individual inter-night variability is present, independent of age, severity and duration of the disease, which should be considered in the clinical evaluation.