The time structure of leg movement activity during sleep: the theory behind the practice

This paper evaluates, in both the theoretical and practical frameworks, the value of the application of the current criteria for the scoring of leg movement activity during sleep, recorded in clinical and research settings, for the study of restless legs syndrome (RLS) and other conditions. Recently, new parameters have been introduced to better describe the time structure of leg movement activity during sleep. The periodicity index, the distribution of inter-movement intervals, and the hourly distribution of periodic leg movements during sleep have emerged as valuable descriptors. Therefore, the additional value provided by the new methods is discussed with a glance at the rationale behind these new approaches. It is concluded that these new methods have proven to be able to provide new insights into the phenomenon of leg movement activity during sleep. In particular, the classical periodic leg movements during sleep (PLMS) index does not seem to be sufficiently specific for the diagnosis and clinical significance of RLS. The specificity of PLMS for the diagnosis of RLS can be significantly increased by considering these additional parameters. The same parameters also allow a more detailed analysis of several aspects of RLS and PLMS that were impossible to perform before on the basis of the simple PLMS index alone.