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Overview

Periodic limb movement disorder (PLMD) and restless legs syndrome (RLS) are distinct disorders, but often occur simultaneously. Both PLMD and RLS are also called (nocturnal) myoclonus, which describes frequent or involuntary muscle spasms. Periodic limb movement was formally described first in the 1950s, and, by the 1970s, it was listed as a potential cause of insomnia. In addition to producing similar symptoms, PLMD and RLS are treated similarly.

Periodic Limb Movement Disorder (PLMD)

Periodic limb movement disorder affects people only during sleep. The condition is characterized by behavior ranging from shallow, continual movement of the ankle or toes, to wild and strenuous kicking and flailing of the legs and arms. Furthermore, abdominal, oral, and nasal movement sometimes accompanies PLMD. Movement of the legs is more typical than movement of the arms in cases of PLMD. Movements typically occur for 0.5 to 10 seconds, in intervals separated by five to 90 seconds.
Today, these parameters are a bit more relaxed, and PLMD usually includes any repetitive, involuntary movement during the night. These limb movements usually occur in deep stage two sleep, but often cause arousal. Thus, PLMD can cause poor sleep, which may lead to sleep maintenance insomnia and/or excessive daytime sleepiness.

The incidence of PLMD 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.

 

Restless Legs Syndrome (RLS)

Restless legs syndrome was described as early as the 16th century but was not studied until the 1940s. People with RLS complain of an irresistible urge to move their legs while at rest. A person with RLS will experience a vague, uncomfortable feeling while at rest that is only relieved by moving the legs. The symptoms of RLS may be present all day long, making it difficult for an individual to sit motionless. Or they may be present only in the late evening. Late evening symptoms can lead to sleep onset insomnia, which tends to compound the effects of RLS. Pregnancy, uremia, and post-surgery conditions have also been known to increase the incidence of RLS. And, surprisingly, fever seems to decrease it.
Although one study found RLS to be most prevalent in middle-aged females, its incidence increases with age.
Restless legs syndrome is estimated to affect 5% of the population. Approximately 80% of people with RLS have PLMD, though most people with PLMD do not experience RLS.


Signs and Symptoms

Periodic Limb Movement Disorder
People with PLMD may be completely asymptomatic, or they may complain of either excessive daytime sleepiness or insomnia, or both. Limb movements can be severe enough to wake an individual from sleep, making it difficult to stay asleep for a significant duration and leading to excessive daytime sleepiness. Many patients who suffer from excessive daytime sleepiness do not know they are being aroused from sleep by periodic limb movements because they do not actually wake up. Rather, they will feel as though they have not slept well. These arousals can occur anywhere from five times an hour up to more than 50 times an hour, depending on the severity of movement.   As mentioned earlier, leg movements in PLMD are typically an upwardly flexed big toe and ankle. Sometimes the hip and knee are flexed and tightened as well.

Because periodic limb movements have been observed in patients with healthy sleep patterns, the claim that they predicate a higher incidence of sleep disorder is controversial. Some studies have shown no greater occurrence of PLMD in patients with insomnia than in those with sleep-wake conditions like excessive daytime sleepiness.

Restless Legs Syndrome
People with RLS find it difficult to keep their legs still and must move them to alleviate the discomfort. The feeling is usually difficult for them to articulate because it is less of a throbbing or stabbing pain and more of a nonspecific discomfort. Many who experience RLS also experience generalized anxiety that results from the incessant need to change the positioning of their legs. Moving the legs, temporarily relieves the discomfort.

The intensity of RLS can vary significantly throughout the day. Many people have no symptoms at all until nighttime, when they attempt to sleep. The discomfort in the legs and the need to move them prevents them from sleeping. Other patients have severe symptoms all day long, which may affect work, travel, or the ability to concentrate.

 

Causes

The causes of Periodic limb movement disorder (PLMD) and restless legs syndrome (RLS) are unknown. The vast majority of PLMD and RLS cases occur independently of other disease processes. It is certain that these conditions often cause insomnia, and some research shows that they might also be caused by other sleep disturbances. This is not likely, however, as PLMD and RLS have not been found to a significant degree in most cases of sleep apnea which seems to precipitate many secondary consequences of sleep disturbance.

There are many conditions that have been associated with PLMD and RLS, including:

  • Chronic renal
  • Myelopathies
  • Peripheral neuropathies
  • Amyloidosis (metabolic disorder of organs and tissues)
  • Diabetes mellitus
  • Anemia and related hemoglobin deficiencies
  • Iron deficiency
  • Vitamin B12 deficiency
  • Uremia (kidney-related toxicity)
  • Chronic lung disease
  • Leukemia
  • Rheumatoid arthritis
  • Fibromyalgia
  • Stiff-man syndrome
  • Isaac's syndrome
  • Huntington's chorea
  • Amyotrophic lateral sclerosis (ALS)

Certain medications may also induce RLS and PLMD, including lithium and antidepressants Withdrawal from other medications, including anticonvulsants, benzodiazepines, and barbiturates may also induce RLS and PLMD.

PLMD
A sleep partner may observe the occurrence of periodic limb movements, which often affect the partner before the patient knows of his or her behavior. In other cases, however, the diagnosis is made by a sleep technician during an overnight polysomnogram, which records sleep and the bioelectrical processes that govern it. This test is often used to assess the cause of excessive daytime sleepiness, such as PLMD and obstructive sleep apnea.


RLS
The diagnosis of RLS is based on the patient's description and personal history of his or her affliction. Because it presents no external secondary symptoms, RLS can be difficult to identify. There are studies designed to quantify the effects of RLS, though these are used mostly for research purposes. For example, a Suggested Immobilization Test, or Forced Immobilization Test, is performed while the patient either voluntarily keeps his or her legs motionless or while the legs are immobilized with a stretcher. The limb movements are then monitored with an EMG. In both PLMD and RLS, a complete examination to exclude secondary causes is warranted.

Furthermore, it is necessary to distinguish PLMD from other more serious types of nocturnal movement, such as seizure. Nocturnal seizures present problems for patients because they can cause injury and are indicative of disorders that require specialized treatment. Also, iron and calcium deficiencies often produce symptoms that mirror RLS, such as leg cramping and tenderness.

 

Treatment

Generally, there are three classes of drugs that are used to treat PLMD and RLS. These are benzodiazepines, Parkinson drugs, and narcotics. Medical treatment of PLMD and RLS often significantly reduces or eliminates the symptoms of these disorders, though not always. There is no cure for PLMD or RLS, and medical treatment must be continued to provide potential relief.
Clonazepam is the most commonly employed benzodiazepine treatment. It is effective in many cases, but not all, and it usually causes drowsiness or sedation. Sometimes, clonazepam allows the patient a better, more restful night's sleep without affecting the occurrence of limb movement. Patients with PLMD may have other sleep disorders, such as obstructive sleep apnea, which the use of clonazepam could worsen.

The drugs used to treat Parkinson's disease are also very effective against PLMD and RLS. These include, L-dopa/carbidopa, bromocriptine (which suppresses the excretion of prolactin), pergolide, and selegiline. If either benzodiazepines or Parkinson's medications do not relieve symptoms, then narcotics, such as codeine, oxycodone, methadone, and propoxyphene are sometimes employed.

In May of 2005, ropinirole HCl (Requip®), which also is used to treat Parkinson's disease, was approved by the Food and Drug Administration (FDA) to treat moderate-to-severe (i.e., 15 or more episodes per month) restless legs syndrome. This medication may result in extreme drowsiness and may cause patients to fall asleep during daily activities (e.g., driving). Other side effects include dizziness, nausea and vomiting, sweating upon standing.