Motor pattern of periodic limb movements during sleep

Background: The pathophysiology of periodic limb movements in sleep (PLMS) in restless legs syndrome (RLS) is unclear. Objective: The authors neurophysiologically investigated PLMS in patients with idiopathic RLS in order to obtain information on the origin and pathophysiology of the movements. Methods: Ten patients with idiopathic RLS underwent electromyography with nerve conduction velocity (EMG-CV), somatosensory evoked potentials (SEPs), transcranial magnetic stimulation (TMS), nocturnal videopolysomnography, and multiple sleep latency test. The authors analyzed 100 consecutive PLMS for each patient to determine how frequently each muscle was involved in the PLMS; how frequently EMG activity started in a given muscle; and the time delay and pattern of activation between the first and theother activated muscles. Results: EMG-CV, SEPs, and TMS findings were all normal; in PLMS, leg muscles were thosemore frequently involved, often with alternation of side. Axial muscles were rarely and upper limb muscles sometimesinvolved. The tibialis anterior was the most frequent starting muscle. There was no constant recruitment pattern from onePLMS episode to another, even in the same patient. There was no ordinate caudal or rostral spread of the EMG activity.Conclusion: The recruitment pattern indicates the engagement of different, independent, and sometimes unsynchronizedgenerators for each PLMS. The authors hypothesize an abnormal hyperexcitability along the entire spinal cord, especiallyits lumbosacral and cervical segments, as the primary cause of PLMS, triggered by sleep-related factors located at asupraspinal but still unresolved level.