PLMS and PLMW in healthy subjects as a function of age: Prevalence and interval distribution

Study Objectives: Several studies have demonstrated a positive correlation between periodic leg movements during sleep (PLMS) and age in healthy subjects. However, little is known about periodic leg movements during wakefulness (PLMW) in this population. Although the definitions of PLMS and PLMW specify a typical intermovement interval of 20 to 40 seconds, scoring criteria allow an intermovement interval of 4 to 90 seconds. The aim of the present study was to look at the prevalence and interval distribution of PLMS and PLMW in relationship with age in a population of healthy subjects. Design: Periodic leg movements were recorded during 1 night. Setting: Sleep laboratory, Hopital du Sacre-Coeur de Montreal. Participants: Sixty-seven healthy subjects aged between 5 and 76 years (32 F, 35 M). Interventions: N/A Measurements and Results: The presence of PLMS was rare before the age of 40, but then the index increased dramatically. PLMW index was higher in younger subjects compared with middle-aged subjects. Interval histograms of PLMS did not revealed a clear peak in younger subjects. With advancing age, PLMS interval histograms show a peak around 15 to 35 seconds, which is not observed in younger subjects. On the other hand, despite high indexes, PLMW interval histograms do not show a clear peak for any age group. Conclusion: These results illustrate that interval evaluation is an important feature of the calculation of periodic movements to discriminate spontaneous motor activity from PLMS or PLMW.