New approaches to the study of periodic leg movements during sleep in restless legs syndrome

Study Objectives: To describe a new approach for the analysis of quantity, type, and periodicity of the leg motor activity during sleep in patients with restless legs syndrome (RLS) and periodic leg movements (PLM). Methods: The following parameters were taken into account for LM: duration, amplitude, area under the curve, sleep stage, side, interval, and bilaterality. The analysis of inter-LM intervals was carried out by drawing their distribution graphs. A new index evaluated their periodicity and was validated by means of a Markovian analysis. The differences in inter-LM intervals, LM duration, and area under the curve between normal controls and patients and between the 3 patient subgroups identified on the basis of their periodicity were statistically analyzed. Setting: N/A Participants: Sixty-five patients with RLS and periodic LM and 22 young healthy controls. Measurements and Results: The RLS patients' inter-LM interval distribution graph showed a wide peak with a maximum located at around 15 to 30 seconds and extending from 10 to 90 seconds, not present in controls, and another peak for intervals less than 8 seconds, higher than that of controls. Three patient subgroups were identified with different proportions of these 2 peaks, periodicity, and Markovian parameters. Periodicity was not dependent on the periodic leg movement index. Patients showing the peak mainly at around 15 to 30 seconds tended to show slightly longer and higher area under the curve LM than did the other 2 subgroups. Conclusions: Our new approach seems to be useful in a new qualitative differentiation among patients with PLM, which is not possible by using the simple PLM index.