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What is periodic limb movement disorder?

Periodic limb movement disorder (PLMD) involves repetitive episodes of muscle movements that usually occur in the legs. The movements are described as a jerking motion or an upward flexing of the feet. The movements happen about every 20 to 40 seconds and occur in clusters lasting from minutes to a few hours.

PLMD is considered a sleep disorder when these movements disrupt sleep and lead to daytime effects such as sleepiness. Most children and adolescents with PLMD are unaware that these movements are taking place.

Many children and adolescents with periodic limb movements in sleep may also experience restless legs syndrome--another movement disorder in which the child or adolescent reports an uncomfortable sensation and irresistible urge to move his or her legs when awake. This urge usually happens in the evenings around bedtime but can occur at other times when the legs have been inactive, such as when sitting still for a long period of time (e.g., during long car rides or while watching a movie).

What causes periodic limb movement disorder?

The exact cause of this disorder is not known. Scientists think PLMD may be related to a low iron level or problems with limb nerve conduction due to diabetes or kidney disease. Though not necessarily a cause, the following are all thought to "influence" or increase the risk of periodic limb movements in sleep:

What are the signs and symptoms of periodic limb movement disorder?

Symptoms of PLMD include:

  • Leg movements. Repetitive leg movements in one or both legs are the classic sign of PLMD. Remember, though, that the child or adolescent experiencing PLMD may be unaware of his or her leg movements since they occur during sleep.
  • Sleep disruption/restless sleep. The frequent leg movements cause disturbed sleep and multiple awakenings. These awakenings are brief and termed "arousals." They can be easily missed by the onlooker but captured on a sleep test by EEG (brain wave) analysis.
  • Daytime sleepiness, behavior and school performance problems. The sleep disruption may cause daytime drowsiness. Many times, children will not appear sleepy but rather they may manifest this as irritability, hyperactivity, and impulsivity.