Periodic limb movements in sleep consist of flexion movements at the ankles, knees and hips, and sometimes the arms, recurring every 10 to 90 seconds, especially during light NREM sleep stages. Though representing an almost obligate accompaniment of restless legs syndrome and frequently associated with various neurologic and physical diseases, they are also widely prevalent among the general population. In this article, the authors examine the clinical significance of periodic limb movements in sleep and advances in understanding the pathophysiology of this phenomenon that, if accompanied by day- or nighttime consequences, is considered to be a disorder (periodic limb movement disorder). They review the treatment options now available, emphasizing that among the different therapeutic strategies, dopaminergic agents in particular have been shown effective in controlled trials. Finally, they discuss the possible role of periodic limb movements in sleep as a risk for cardiovascular consequences.
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• Periodic limb movements are repetitive flexion movements of the toes, ankles, knees, and hips, sometimes the upper limbs too, lasting from 0.5 to 10 seconds that recur primarily in stage N1 and stage N2 of sleep with a periodicity ranging from 10 to 90 seconds.
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• Periodic limb movements may be associated with no EEG changes or with EEG evidence of arousal or other transient activities, such as bursts of delta waves, and are preceded and associated with autonomic activation.
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• Periodic limb movements in sleep tend to occur more frequently in the elderly population, and have been reported associated with several other medical conditions, but are especially frequent in restless legs syndrome.
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• Periodic limb movement disorder is diagnosed when movements occur at a rate of more than 5 per hour in children or 15 per hour in adults, causing clinically significant sleep disturbance or impairment in mental, physical, social, occupational, educational, behavioral, or other important areas of functioning.
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• Periodic limb movements in sleep respond to dopaminergic treatment.
Historical note and terminology
The first clinical description of periodic limb movements in sleep was reported by Symonds in 1953 (181). He coined the term “nocturnal myoclonus” and described 5 patients who complained of recurrent episodes of involuntary jerking or twitching of the limbs, occurring during sleep, at the moment of falling asleep, or during relaxing wakefulness. Symonds supposed that the nocturnal myoclonus might represent an epileptic syndrome, maybe familial (181). In 1965 Lugaresi and associates first described the polysomnographic characteristics of nocturnal myoclonus in a series of patients with restless legs syndrome (117), and in 1966 they noted that nocturnal myoclonus might be present also as an isolated symptom (115), and subsequently in the 1970s and 1980s Coleman pointed out that it could be associated to a variety of clinical conditions other than restless legs syndrome (34). Moreover, because nocturnal myoclonus tends to occur periodically at 20- to 40-second intervals in sleep and is rarely myoclonic (less than 250 msec) during sleep, Coleman suggested to name it as “periodic movements in sleep” (34). Only later were the terms “periodic leg movements in sleep” and “periodic limb movements in sleep” introduced.
Two sets of scoring rules have been proposed in the last decades: the first by the International Restless Legs Syndrome Study Group (IRLSSG) and the World Association of Sleep Medicine (WASM) and the second by the American Academy of Sleep Medicine (AASM) (212; 17). The WASM rules have been updated integrating with the data obtained from studies that have better characterized the features of periodic limb movements in sleep (55).
The term “periodic limb movement disorder” is referred by the American Academy of Sleep Medicine to a specific sleep-related movement disorder characterized by: (A) polysomnography demonstrates periodic limb movements in sleep, as defined in the American Academy of Sleep Medicine Manual for the Scoring of Sleep and Associated Events (16); (B) the frequency is greater than 5 per hour in children or greater than 15 per hour in adults; (C) the periodic limb movements in sleep cause clinically significant sleep disturbance or impairment in mental, physical, social, occupational, educational, behavioral, or other important areas of functioning; and (D) the periodic limb movements in sleep and the symptoms are not better explained by another current sleep disorder, medical or neurologic disorder, or mental disorder (eg, periodic limb movements in sleep occurring with apneas or hypopneas should not be scored) (07).