Assessment of Periodic Leg Movements Is an Essential Component of an Overnight Sleep Study

Arthur S. Walters

New Jersey Neuroscience Institute at JFK Medical Center, Edison, New Jersey, Department of Neuroscience, School of Graduate Medical Education, Seton Hall University, South Orange, New Jersey, Department of Neurology, UMDNJ-Robert Wood Johnson, Medical School, Piscataway, New Jersey

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First, recording of leg movements by electromyogram (EMG) during polysomnography is necessary to distinguish periodic limb movements (PLMs) in sleep from other involuntary movements in sleep that warrant treatment. History alone is not sufficient to determine whether PLMs in sleep are present (1, 2) and many other sleep-related movement disorders, such as the rapid eye movement (REM) sleep behavior disorder, have characteristic EMG patterns that for proper diagnosis necessitate the use of leg and arm EMG electrodes during polysomnography. Although these other sleep-related movement disorders are often suspected by history, there are times when they are unsuspected. Leaving off the leg EMG electrodes would mean missing at least some cases of these other important sleep-related diagnoses (3).

Second, if patients have isolated PLMs in sleep they should be documented by EMG on polysomnography and treated if the spouse bringing in the patient to see the physician complains that the patient's leg kicking interferes with the sleep of the spouse. Treatment of the PLMs in sleep of the patient will allow the patient and spouse to sleep together peacefully throughout the night.

Third, recording of leg movements by EMG during polysomnography is necessary to document PLMs during wakefulness in the restless legs syndrome. I would first like to make it clear to readers that PLMs in sleep is not the same as restless legs syndrome. In restless legs syndrome, patients sleeplessly walk the floor at night because of leg discomfort (4). Although about 80-87% of patients with restless legs syndrome have PLMs in sleep (5), it is also true that PLMs in sleep commonly occur without restless legs syndrome. Most patients with restless legs syndrome also have PLMs in wakefulness that are elicited by having the patient lie perfectly still and recording the leg movements during polysomnography with EMG (suggested immobilization test) (6). Although 90% of patients with restless legs syndrome come to me with a chief complaint of insomnia due to leg discomfort, about 10% come to me with a chief complaint of insomnia due to leg twitching during wakefulness (PLMs in wakefulness). Restless legs syndrome, PLMs in sleep, and PLMs in wakefulness are all treated the samewith dopaminergic drugs, opioids or benzodiazepines (3). Treatment of the leg discomfort and PLMs in wakefulness in patients with restless legs syndrome curtails the associated insomnia and allows patients to function normally at work and in their home environment.

Fourth, it is well known that pseudo-PLMs in sleep may arise as arousal phenomena after cyclically occurring apneas and these must be distinguished from true PLMs in sleep. Exer and Collop have suggested that PLMs in sleep-like movements may also be associated with more subtle, difficult to identify forms of sleep-disordered breathing such as the upper airway resistance syndrome. They further suggest that PLMs in sleep may be used as a way of helping identify the upper airway resistance syndrome (7).

Fifth, patients with certain psychiatric disorders have a higher prevalence of PLMs in sleep. After our discovery that PLMs in sleep occur more commonly in children with attention-deficit hyperactivity disorder (1, 2), Chervin and Archbold examined the relationship between PLMs in sleep and attention-deficit hyperactivity disorder in children with sleep apnea (8). The rate of PLMs in sleep showed a linear association with hyperactivity among those subjects with sleep-disordered breathing, implying that PLMs in sleep are causitive to some cases of attention-deficit hyperactivity disorder. This alone would warrant their being recorded in this patient group. However, further research needs to be done to determine whether PLMs in sleep are a cause/aggravating factor of the symptoms of attention-deficit hyperactivity disorder or are merely a marker for the disorder. This applies equally to the association of PLMs in sleep with other psychiatric disorders such as posttraumatic stress disorder and depression (9, 10). It is conceivable that the constant sleep fragmentation from PLMs in sleep over the years might lead to depression and that treatment of the PLMs in sleep might lead to a remission of the depression.

Sixth, recording of PLMs in sleep may provide a unique prognostic indicator of mortality in renal failure. In one study of patients with end-stage renal disease, the 20-mo survival rate with less than 20 PLMs/h of sleep was greater than 90% versus 50% with more than 20 PLMs/h of sleep. The median survival of patients with more than 80 PLMs/h of sleep was only 6 mo (11). Erythropoietin reduced the number of PLMs per hour of sleep in hemodialysis patients (12).

Seventh, there may be a relationship between PLMs in sleep and hypertension and cardiovascular disease. A single patient with congestive heart failure, insomnia, and severe PLMs in sleep had resolution of the congestive heart failure, insomnia, and PLMs in sleep after heart transplantation (13). In a follow-up study, 52% of 23 men with severe congestive heart failure and only 11% of 9 healthy control subjects had a PLM index in the moderately severe range of >25/h of sleep (14). Eighteen percent of 91 subjects with hypertension had PLMs in sleep and the prevalence of PLMs in sleep was directly proportional to the severity of the hypertension. Patients with Grade III hypertension had a 36.4% prevalence of PLMs in sleep as opposed to a 13% prevalence in patients with Grade I and II hypertension (15). Tachycardia accompanies PLMs in sleep and there appears to be a hierarchy of arousals accompanying the PLMs in sleep, going from autonomic activation to bursts of delta activity to alpha activity to a full awakening. When PLMs in sleep were accompanied by theta or alpha activity the heart rate was even faster (16,17). Rises in blood pressure on the order of 23% have also been found to accompany PLMs in sleep in a single patient (18). Finally, vasoconstriction, cold feet, and decreased peripheral pulses may be associated with PLMs in sleep (19, 20). Whether the temporary rises in heart rate and blood pressure that accompany PLMs in sleep have any ultimate cardiovascular consequences or whether they are merely consequences of autonomic arousal that accompany the PLMs in sleep needs further investigation.

	References

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