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 neurophy siologically investigated PLMS in patients with idiopathic RLS in order to obtain information on the origin and pathophysiology of the movements. Meth ods: Ten patients with idiopathic RLS underwent electromyography with nerve conduction velocity (EMG-CV), somatosensory evoked potentials (SEPs), tran scranial magnetic stimulation (TMS), nocturnal videopolysomnography, and mu ltiple sleep latency test. The authors analyzed 100 consecutive PLMS for ea ch 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 the other activated muscle s. Results: EMG-CV, SEPs, and TMS findings were all normal; in PLMS, leg mu scles were those more frequently involved, often with alternation of side. Axial muscles were rarely and upper limb muscles sometimes involved. The ti bialis anterior was the most frequent starting muscle. There was no constan t recruitment pattern from one PLMS episode to another, even in the same pa tient. There was no ordinate caudal or rostral spread of the EMG activity. Conclusion: The recruitment pattern indicates the engagement of different, independent, and sometimes unsynchronized generators for each PLMS. The aut hors hypothesize an abnormal hyperexcitability along the entire spinal cord , especially its lumbosacral and cervical segments, as the primary cause of PLMS, triggered by sleep-related factors located at a supraspinal but stil l unresolved level.