Measurement of periodic leg movements during sleep and wakefulness

Periodic leg movements (PLM) are repetitive limb movements that usually occur during sleep (PLMS), but can also occur while individuals are awake (PLMW), especially in patients with restless legs syndrome (RLS). The standard criteria indicate that leg movements (LM) are scored as PLM when the electromyographic signal derived from the tibialis anterior shows activations longer than 0.5 and shorter than 10 seconds, separated by an inter-movement interval ranging from 5 to 90 s from each other, and occurring in series of at least 4. The main parameter obtained by these criteria is the number of PLM per hour of sleep or wakefulness (PLMS index or PLMW index). The new rules for PLM scoring represent an evolution from the previous ones because they take into consideration amplitude, duration and frequency criteria that in the past were a matter of confusion. Today, three additional parameters (total LM index, periodicity index, and time distribution), besides the classical PLMS index, offer an important help to support the diagnosis of RLS.