What is Nocturnal Myoclonus?

Emma Lloyd

Nocturnal myoclonus, also known as periodic limb movement disorder or PLMD, is a form of myoclonus in which the symptoms of the disorder are experienced during sleep. Myoclonus is itself a disease symptom, rather than a diagnosis, which manifests as sudden muscular contractions or muscular relaxation. Muscular contraction or relaxation can occur in response to a trigger, or may occur randomly. Occasional involuntary muscle twitches and hiccups are examples of non-disordered myoclonus.

Nocturnal myoclonus affects people in their sleep.
Nocturnal myoclonus affects people in their sleep.

Many people who experience nocturnal myoclonus do not have accompanying negative side effects. They may simply move their limbs during sleep without being disturbed by the movement. In these cases the person is said to have periodic limb movements during sleep, or PLMS. This is not the same as PLMD, as PLMS is not a disorder in itself, and does not always require treatment. PLMS is, however, a symptom of PLMD.

Nocturnal myoclonus can cause insomnia.
Nocturnal myoclonus can cause insomnia.

Nocturnal myoclonus is classified as a sleep disorder, and can cause symptoms during the night as well as side effects during waking hours. The disorder can cause nighttime sleep disturbance, insomnia, and sleepiness during waking hours.People who experience multiple episodes of periodic limb movements during sleep over several nights, as well as sleep disturbance and side effects during waking hours, may be diagnosed with PLMD.

Snoring is a risk factor for nocturnal myoclonus.
Snoring is a risk factor for nocturnal myoclonus.

Diagnosis of PLMD is made on the basis of anecdotal evidence from a patient’s partner or other close relatives or friends, as well as the results of a polysomnography. The polysomnography, or sleep study, is a test which records the biological and physiological changes that occur when a person is asleep. The test is carried out during a patient’s normal sleeping hours and records brain function, eye movements, muscle activity, and heart rhythm.

An estimated 4% of people are affected by PLMS. The percentage increases with increased age, and women are more likely to be affected than men. Up to 11% of elderly women may be affected. There is also evidence that PLMS is related to restless leg syndrome. One study has found that up to 80% of people with restless leg syndrome also had PLMS.

Risk factors for nocturnal myoclonus, particularly in the absence of restless leg syndrome, are varied. These include drinking coffee, snoring, stress, the use of hypnotics, and being a shift worker. Several risk factors are associated with restless leg syndrome as well as PLMD, including obstructive sleep apnea, musculoskeletal disease, heart disease, catalepsy, and mental disorder.

Treatments for nocturnal myoclonus are targeted to reducing incidences of leg jerking caused by muscular contraction or relaxation, and reducing incidence of being woken during sleep. Dopaminergic medications, which are drugs capable of stimulating dopamine receptors, are useful in treating both symptoms. Low doses of a medication called Clonazepam® can also help improve sleep quality.

Up to 11% of elderly women are afflicted with periodic limb movement disorder, more than any other demographic.
Up to 11% of elderly women are afflicted with periodic limb movement disorder, more than any other demographic.

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Discussion Comments


@discographer-- You're referring to atonia which is a state when muscles are extremely relaxed during REM sleep so that movement doesn't occur. People with nocturnal myoclonus don't experience movement in REM sleep either. They only experience involuntary movement during other sleep stages. So this doesn't apply to them.


Involuntary actions like contractions are one thing, but I don't think that it's normal for anyone to move their limbs at night.

I read a little bit about this for one of my classes. Our nervous system actually has a mechanism which causes our muscles to lock-down when we are asleep. This is precisely to prevent any kind of movement when we are dreaming etc. If we didn't have this mechanism, we would all be sleepwalking, kicking our partner in bed and possibly getting hurt too.

I don't know anyone who has nocturnal myoclonus but it must have a connection with this mechanism I described. It's probably just not working right for some reason and it should definitely be looked into.

Have there been any studies done on the incidence of sleepwalking in individuals with nocturnal myoclonus? Does anyone know?


I used to experience muscle contractions and twitching at night before. It hasn't happened lately. At that time, my doctor thought that it was probably due to vitamin deficiency and asked me to take a multi-vitamin regularly. He was right because the contractions and twitching would go away after taking vitamins and I haven't experienced them lately at all.

I have no idea if vitamin deficiency could be a factor affecting nocturnal myoclonus but it's probably worth asking the doctor about it.

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