Periodic arousals or periodic limb movements during sleep?

Periodic limb movements during sleep (PLMS), frequently found in polysomnograms, are often accompanied by arousals. The relationship is not clear, however, because PLMS can occur before, after or simultaneous to the electromyographic (EMG) activation. We describe the case of a patient who presents PLMS during two of three consecutive recording nights, and periodic arousals without motor activation on the other night. We conclude that, at least in some patients with a periodic limb movement disorder, there exists an underlying arousal disorder that produces periodic activation and deactivation of the cerebral cortex.