Periodic Limb Movement Disorder (PLMD), sometimes called nocturnal myoclonus, is a common parasomnia that affects up to 40% of people older than 65 years of age and 11% of sleep disorder clinic patients who complain of insomnia.
PLMD manifests as brief (0.5 to 5.0 seconds), stereotypic, and involuntary contractions of the lower limbs (often the dorsiflexors of the foot and flexors of the lower legs), at intervals of 20 to 40 seconds. Contractions appear more commonly during NREM stages 1 and 2. Although patients are unaware of them, the EEG demonstrates nocturnal arousals and actual awakenings. Sleep is often unrefreshing, with hypersomnia is the most common complaint.