Periodic Limb Movement Disorder (PLMD) is a leg disorder that is similar to Restless Legs Syndrome but is exhibited during sleep rather than while awake. Periodic limb movements usually occur in the legs but may also affect the arms, and are involuntary (not consciously controlled). An observer might describe them as a “jerk” or “kick”. As the name implies, the movements occur at periodic (regular) intervals with 20-40 seconds separating each kick, and a series of at least 4 jerks must be seen in order to diagnose PLMD (frequently many more than 4 kicks are seen in a row). The movements usually do not occur continuously throughout sleep, but instead cluster in the first half of the night. Since a certain number of periodic limb movements occur in normal sleeping individuals, PLMD is only diagnosed with 5 or more occur per hour of sleep, averaged over the entire night.
Periodic limb movements are different from the “hypnic jerk”, a sudden movement of the entire body usually accompanied by the sensation of falling that takes place soon after sleep begins. Hypnic jerks are quite normal and usually do not interfere with sleep quality or cause daytime symptoms.
Individuals with PLMD may be awakened by leg movements occurring immediately after falling asleep, and awaken so quickly that they may not realize that they were asleep. These patients may complain of difficulty falling asleep. Other patients may report difficulty staying asleep, and may in fact be experiencing leg movements throughout the night that are accompanies by “microarousals” (very brief awakenings) that create an overall feeling of a poor night’s sleep or sleeping very little. Other individuals with PLMD may have only a general complaint of restless or poor sleep.
Some people may not be aware of any nighttime disturbance, but the many brief awakenings do disturb sleep and cause excessive daytime sleepiness. These individuals might have no complaint about sleep at night, but fall asleep during the day, while reading, watching TV, working or driving. Children often react to sleepiness by becoming hyperactive, and thus young persons with PLMD may appear hyperactive or inattentive, and may even be diagnosed with ADHD.
Periodic limb movements may cause problems that affect the bed partner rather than the patient. Such complaints may include being kicked at night, or the bed covers being twisted or being knocked off the bed, or that limb movements shake the bed.
What to Do
Periodic limb movement disorder often requires more extensive study to make a proper diagnosis. People with PLMD usually do not feel their nighttime movements and may complain only of restless sleep or excessive daytime sleepiness. Overnight sleep testing in a sleep clinic is commonly used to diagnose PLMD.
If you think you suffer from PLMD, speak to your health care provider or one of our board certified sleep specialists, who can help you determine your next steps.