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The common conception of sleep holds that it’s peaceful and a time when the body is calm and fully at-rest. But for people with Periodic Limb Movement Disorder (PLMD), that notion of sleep is far removed from their reality.
PLMD arises when frequent, repetitive motions during sleep, such as jerking or twitching of the legs, cause a person’s sleep to become disturbed. It can prevent them from getting sufficient rest and lead to significant daytime drowsiness.
PLMD often arises in patients who have Restless Leg Syndrome (RLS), another movement-based sleep disorder. Both independently and together, these conditions can induce sleep deprivation and its attendant health consequences.
This guide offers a detailed look at PLMD. It reviews how it is defined, how it is related to RLS, its most frequent symptoms, what causes it, and how it is diagnosed and treated.
What Are Periodic Limb Movements and Periodic Limb Movement Disorder?
Periodic limb movements are slight motions in the arms or the legs. These movements are much less pronounced than stretching or changing one’s posture or sleeping position. They most often take the form of what seems like fidgeting, such as
- Extending the big toe
- Tightening a muscle
- Lightly flexing a joint like the knee or ankle
The movements normally affect both legs, but they can affect just one. In addition, though the majority of periodic limb movements happen in the legs, they can occur in the arms as well. Examples include minor flexion or extension of the elbow, wrist, or fingers.
If these twitches happen while you’re asleep, they are known as periodic limb movements while you sleep (PLMS), and if you’re not sleeping, they are periodic limb movements while you’re awake (PLMW). PLMW are rare and usually connected to more serious instances of involuntary muscle movements.
PLMS are common, and for most people, don’t cause any problems. The majority of the time, sleepers are unaware that PLMS are even happening, and as a result, they are of little import. In some cases, though, PLMS are more frequent and cause sleep disturbances. When this happens, the presence of PLMS becomes a sleep disorder known as Periodic Limb Movement Disorder.
Myoclonus is the technical term for twitching or jerking muscles, so in the past, PLMD was known as sleep myoclonus or nocturnal myoclonus. PLMD is the preferred contemporary medical terminology as determined by the World Health Organization’s 11th Revision of the International Classification of Diseases (ICD-11) and the Third Edition of the International Classification of Sleep Disorders (ICSD-3) from the American Academy of Sleep Medicine (AASM).
In people with PLMD, the twitching usually takes place during episodes that range from minutes to an hour in length. During the episode, each movement lasts for one to five seconds. Movements normally recur every 20 to 40 seconds, but this interval between them can stretch from 5 to 90 seconds. Episodes are most likely to occur during the first half of the night while you are in light, non-REM (Rapid Eye Movement) stages of sleep.
Movements associated with PLMD tend to be repetitive, so during an episode, it’s likely that a person will twitch or move in the same way. However, people with PLMD may have different movements from one night to the next.
How Common is Periodic Limb Movement Disorder?
There is no definitive data about the prevalence of Periodic Limb Movement Disorder. A study conducted in Europe estimated that 3.9% of the population has PLMD. Others place the prevalence at closer to 6%.
PLMD appears to be more common as people get older as most cases arise in people who are in middle or older age. Some studies have found it to be more common in women while other studies have found no association with gender.
What is the Relationship Between Periodic Limb Movement Disorder and Restless Leg Syndrome?
PLMD often accompanies other sleep disorders, most notably Restless Leg Syndrome. RLS is a condition in which a person feels extremely strong urges to move the arms or legs when they are lying in bed. It is estimated that at least 80% of people who have RLS also experience periodic limb movements during sleep.
Given this strong association, it is common for people to wonder about the difference between Periodic Limb Movement Disorder and Restless Leg Syndrome. There are a few important ways in which they are distinct:
- RLS occurs while a person is awake. PLMD occurs during sleep.
- RLS involves a strong sensation in the limbs that compels a person to move. PLMD generally happens without a person being aware of it and does not involve perceived sensations in the limbs.
- With RLS, sensations are involuntary, but movements in response to the sensations, such as stretching or getting up and walking around, are voluntary. With PLMD, the movements are less pronounced and happen involuntarily.
People who have both RLS and PLMD can find these conditions to be a significant barrier to obtaining a good night’s sleep. The discomfort from RLS can make it hard to get comfortable in bed, and once asleep, PLMD can cause sleep disruptions. During those awakenings, the symptoms of RLS may make it harder to get back to sleep.
Because so many patients with RLS have PLMD, many experts believe that they stem from a related underlying problem affecting the nervous system. However, they are distinct conditions, and though it is not as common, there are patients who have PLMD without RLS. In addition, as explained in a later section, the diagnostic process is different for the two conditions.
Can Periodic Limb Movement Disorder Affect Children?
As in adults, PLMD in children is typically closely associated with RLS. These disruptive movements can also be related to other health conditions, including sleep apnea or a neuropsychiatric issue.
What Are the Symptoms of Periodic Limb Movement Disorder?
The most obvious symptom of PLMD is the repetitive movement itself; however, these movements aren’t perceived by the sleeper. This means that patients usually only become aware of the movements when they are informed by someone with whom they share the bed.
In PLMD, the frequency of limb twitching is high enough to cause sleep disruptions. For this reason, patients often report having fragmented sleep with multiple nighttime awakenings. Not surprisingly, this is regularly experienced along with symptoms like excessive daytime sleepiness and fatigue.
What Are the Health Consequences of Periodic Limb Movement Disorder?
It can be discomforting to be awoken by your own periodic limb movements or to witness another person who is experiencing these jerks and twitches, and it is natural to want to know whether periodic limb movements are harmful or dangerous.
Periodic limb movements during sleep are normally innocuous. Most people have these twitches from time to time without knowing it or having their sleep disturbed.
Periodic Limb Movement Disorder, on the other hand, can have harmful health consequences. Because they are awoken by the movements, people who have PLMD may have chronic insomnia and sleep insufficiency. The negative implications of sleep deprivation are serious and take a toll on immune function, metabolism, the endocrine system, emotional well-being, and brain health.
Daytime sleepiness from PLMD can be detrimental to academic performance and work productivity. It can raise a person’s risk of being involved in a car accident, falling, or suffering another type of unintentional injury.
In some cases, there may be health effects from an underlying medication condition that causes periodic limb movements. Examples of some of these conditions include diabetes and anemia.
What Are the Causes of Periodic Limb Movement Disorder?
Researchers have not yet been able to identify exactly what causes Periodic Limb Movement Disorder. Because of its connection with RLS, it is thought to relate to a problem in the nervous system, but to date, no clear mechanism for explaining the condition has been identified.
When a causal explanation for a condition cannot be found, experts utilize observational studies to try to find patterns to identify who is most likely to develop that condition. These studies compare the prevalence of other conditions in patients with PLMD versus their prevalence in the general public. If rates are higher in people with PLMD, it indicates that there may be a link between them.
While the findings of these studies can help estimate who may be at a higher risk of PLMD, they are not a prediction or surefire way of knowing who will develop the condition and who will not. Instead, it is most helpful to think about these as risk factors, which are things that might increase a person’s likelihood of having PLMD but do not assure that a person will have it.
Based on the studies conducted so far, the clearest risk factor for PLMD is having Restless Leg Syndrome. People with other sleep disorders, including narcolepsy, obstructive sleep apnea, and REM sleep behavior disorder, also frequently have PLMD.
Other things that have been found to be associated with higher rates of PLMD include:
- Iron deficiency
- Use of certain drugs including some stimulants, antipsychotics, antidepressants, and antihistamines
- Stopping using some drugs, including benzodiazepines
- Spinal cord injury
- Conditions that damage nerves including Parkinson’s disease, multiple sclerosis (MS), and multiple system atrophy
- Chronic kidney problems
- Chronic liver problems
- Sleep-Related Eating Disorder (eating during sleep)
Again, it is important to note that having one or more of these risk factors does not mean that a person will develop PLMD. Anyone who is concerned about their risk or about the quality of their sleep should talk with their doctor for the most tailored medical advice.
How is Periodic Limb Movement Disorder Diagnosed?
Most people with PLMD first go to the doctor because they are experiencing excessive daytime sleepiness and/or they have noticed that their sleep is marked by numerous awakenings. They may also have been told by a partner that they are moving or twitching repeatedly while asleep. When PLMD is suspected by the doctor, it is usually because of a partner’s reports or because the patient has already been diagnosed with RLS.
At the doctor’s office, the diagnostic process begins by reviewing the patient’s symptoms and discussing any potentially relevant aspects of their medical history. The doctor may request that they keep a sleep journal that logs daily bedtime, wake-up time, and any nighttime arousals. Periods of daytime drowsiness might be noted in the journal as well. Keeping this type of journal for a period of a week or more can help identify patterns related to the patient’s sleeping problems.
A formal diagnosis of PLMD requires polysomnographic testing. This is a sleep study that takes place overnight in a specialized clinic. During the test, electrodes monitor muscle activity, breathing, heart rate, and eye movement. People with PLMD usually have abnormal spurts of muscle activity during the sleep study.
Observing the patient’s breathing during polysomnography helps determine whether obstructive sleep apnea is a possible contributing factor to their sleeping problems. Doctors may order other types of tests, such as blood or urine tests, to check for potential issues that could play a role in periodic limb movements.
This diagnostic process is one area of divergence between Restless Leg Syndrome and Periodic Limb Movement Disorder. The diagnosis of RLS can be made solely based on the patient’s history, but PLMD requires polysomnography. Even though an overnight sleep study is not necessary to diagnose RLS, this test is frequently ordered after RLS has been diagnosed to determine if a patient also has PLMD.
How is Periodic Limb Movement Disorder Treated?
Treatment for Periodic Limb Movement Disorder is tailored to each individual patient and can involve multiple different elements. PLMD generally cannot be cured, so the goal of treatment is to eliminate or reduce its symptoms. The most common components of treatment are described in the subsequent sections.
Treating Associated Health Conditions
If PLMD is associated with RLS, therapy usually focuses on RLS and tends to help resolve problems with PLMD as well. If other underlying issues that may contribute to PLMD — such as anemia, sleep apnea, or kidney problems — can be managed effectively, PLMD-specific therapy may not be necessary.
Behavior modifications can help reduce the severity of PLMD. Examples of these behavior changes can include:
- Avoiding caffeine and other stimulants, especially close to bedtime.
- Reviewing daily medications with the doctor to consider changing drugs or dosages if those prescriptions could be contributing to PLMD.
- Eating a balanced diet that includes a complete slate of nutrients, vitamins, and minerals.
- Getting regular exercise, especially lower-body conditioning, during the day.
- Practicing meditation and/or other strategies for relaxation and diverting focus, especially for people with RLS. This may help with sleep onset or with getting back to sleep after nighttime awakenings.
- Improving sleep hygiene by normalizing sleep habits and optimizing the sleep environment. A bedroom that is conducive to sleep may help people with PLMD who wake up in the night to get back to bed more easily.
A number of different medications may be prescribed to treat both Periodic Limb Movement Disorder and Restless Leg Syndrome.
Many of the most-utilized drugs for PLMD are drugs that are primarily used to treat Parkinson’s disease, and they work by replacing a substance in the brain called dopamine. These medications help many patients, but they can cause worse symptoms before administration of the next dose or when the drug is stopped. Depending on the drug, they may cause other side effects as well.
Other drugs that may be used include anti-seizure drugs (known as anticonvulsants), opioid painkillers, benzodiazepines, and sleeping tablets. All of these can cause side effects, so in each patient’s case, the doctor is in the best position to review the potential benefits and risks of any specific medication.
Iron supplementation may be prescribed as a medication if this is suspected as an underlying issue that is aggravating PLMD. Iron supplements may be taken orally or intravenously, but they should be administered in conjunction with a health professional to avoid possible iron overload.
One small study found that magnesium supplements could reduce PLMD symptoms. While this is a promising avenue for future research, there is insufficient data at this time to consider this as a standard or proven therapy. Similarly, there are no well-studied or proven natural remedies for PLMD. As there can be side effects from magnesium supplements or other natural remedies, these should only be taken after first consulting with a doctor.