Periodic Limb Movement Disorder (PLMD)

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.

Periodic Limb Movement Disorder (PLMD) vs. Restless Legs Syndrome (RLS)

Up to 90% of individuals diagnosed with Restless Leg Syndrome have Periodic Limb Movements (PLMs) when sleep recordings are taken over multiple nights. Asymptomatic PLMs does not require treatment. Restless Legs Syndrome (RLS) refers to the symptom, while Periodic Limb Movements (PLMs) refers to the sign. Periodic Limb Movements Disorder (PLMD) is a diagnosis is based on polysomnography findings. The difference between Periodic Limb Movements Disorder (PLMD) and Restless Leg Syndrome (RLS) is that PLM is an involuntary action. The patient often sleeps through an episode of leg movements. In RLS, however, patients are awake the whole time and are jerking or kicking their legs in an effort to overcome the discomfort their brains are perceiving. In summary, RLS keeps the patient awake, but PLM occurs when the patient is already asleep.
  • PLMS > 10 per hour is indicative of RLS