Periodic limb movement disorder

Periodic Limb Movement Disorder (PLMD), also called nocturnal myoclonus, is a sleep disorder where the patient moves involuntarily during sleep. It can range from a small amount in the ankles and toes to wild flailing of all four limbs. These movements, which are more common in the legs than arms, occur for between 0.5 and 10 seconds, recurring at intervals of 5 to 90 seconds. A formal diagnosis of PLMD requires three periods during the night, lasting from a few minutes to an hour or more, each containing at least 30 movements followed by partial arousal or awakening.

PLMD is a cause of insomnia and daytime sleepiness. The incidence of this disorder increases with age. It is estimated to occur in 5% of people age 30 to 50 and in 44% of people over the age of 65. As many as 12.2% of patients suffering from insomnia and 3.5% of patients suffering from excessive daytime sleepiness may experience PLMD.

It is related to restless leg syndrome (RLS) in that 80% of people with RLS also have PLMD. However, most people with PLMD do not experience RLS.

This disorder has made its way into popular culture, being referred to as "jimmy legs" and "jimmy arms" in an episode of Seinfeld, and has been known to cause couples to sleep in separate beds, as seen in I Love Lucy. In both examples, one subject suffers from PLMD severely enough to disturb the sleep of the other subject.