Nocturnal myoclonus

Overview
Periodic Limb Movement Disorder (PLMD), also called nocturnal myoclonus, is a sleep disorder where the patient moves limbs involuntarily during sleep and has symptoms or problems related to the movement. If the patient moves limbs during sleep but there are no consequences, it is simply called periodic limb movements of sleep (PLMS). Not all patients with PLMS have PLMD (in fact, most people with PLMS do not have a disorder requiring any treatment).

PLMS is diagnosed with the aid of a polysomnogram or PSG. PLMD is diagnosed by first finding PLMS on a PSG, then integrating that information with a detailed history from the patient and/or bed partner. PLMS can range from a small amount of movement 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 5 seconds, recurring at intervals of 5 to 90 seconds. A formal diagnosis of PLMS 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.

PLMS can cause 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 (which means it is a normal observation in most individuals). As many as 12.2% of patients suffering from insomnia and 3.5% of patients suffering from excessive daytime sleepiness may experience PLMS.

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

PLMS 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. In both examples, one subject suffers from PLMS severely enough to disturb the sleep of the other subject.

Treatment
Nocturnal myoclonus was discovered by Mary Jane Stout. Nocturnal myoclonus is treated by medications aimed at reducing or eliminating the leg jerks or the arousals. Non-ergot derived dopaminergic drugs (pramipexole and ropinirole) are preferred. Other dopaminergic agents such as co-careldopa, co-beneldopa, pergolide, or lisuride may also be used. These drugs decrease or eliminate both the leg jerks and the arousals. These medications are also successful for the treatment of RLS restless leg syndrome.

In one study, co-careldopa was superior to dextropropoxyphene in decreasing the number of leg kicks and the number of arousals per hour of sleep. However, co-careldopa and, to a lesser extent, pergolide may shift the leg movements from the nighttime to the daytime.

Clonazepam, (Klonopin), in doses from 2 to 8 mg at bedtime, has been shown to significantly reduce leg kicks in a patient who had nocturnal myoclonus to the degree that leg and knee pain persisted throughout the next day.