What Is Sleep Myoclonus or Involuntary Muscle Twitching Movements?

Sudden Jerking Movements or Muscle Spasms May Occur in Sleep

A sleeping baby may experience sleep myoclonus as a sudden, involuntary twitching or jerking movement affecting the muscles of the body
A sleeping baby may experience sleep myoclonus as a sudden, involuntary twitching or jerking movement affecting the muscles of the body. Credit: Getty Images

What is the definition of the term sleep myoclonus? How does it differ from other involuntary muscle movements that cause jerking or twitching out of sleep? If you have ever seen your infant or baby child jerk suddenly during sleep, you may want to learn about sleep myoclonus, as it may affect children more commonly. The condition can also affect adults, however.

What Is the Definition of Sleep Myoclonus?

Sleep myoclonus is a condition in which there is a sudden jerking or twitching movement that affects a muscle and occurs during sleep. It is involuntary, meaning that it is not under conscious control and not done on purpose. It may affect smaller muscles or even cause movements of the extremities (arms or legs). It may appear like a sudden twitching in an infant or baby, and this may lead to confusion about the possibility of a seizure.

Nocturnal myoclonus, also known as periodic limb movement disorder (PLMD), involves repetitive movements of the legs during sleep or even wakefulness. It may occur multiple times per minute. It can affect extremities in an alternating pattern. It usually affects both sides equally and causes a flexion of the fingers, wrists, elbows, and occasionally feet. It may occur repeatedly, but also go away for extended periods during the night. Sleep myoclonus happens during the early stages of sleep and it may be provoked by stimulus.

The Occurrence of Sleep Myoclonus in Children

As noted, myoclonus is a condition that may cause concern when it occurs in children as it may seem like a seizure or infantile spasms. The important difference is that sleep myoclonus only occurs in sleep.

It often develops during the first week of life and it frequently resolves by itself within one year. There are no adverse consequences, so it is commonly called benign neonatal sleep myoclonus. Infants who experience this will have a normal neurologic examination and EEG.

If these movements occur during wakefulness, further evaluation by your child's doctor may be necessary. Sleep myoclonus is sometimes confused with a seizure.

How Is Nocturnal Myoclonus Different from Seizures?

Although the cause is not clear, nocturnal myoclonus may involve problems with a neurotransmitter called dopamine this is unlike seizures, which involve electrical changes in the brain. Myoclonus, for adults, also may result as a side effect to some drugs, including levodopa, cyclic antidepressants and bismuth salts.

The condition often improves after a patient stops taking the drug causing the problem. If you suspect this is your problem, talk to your doctor before abruptly stopping any medication, however.

In benign neonatal sleep myoclonus, the jerking movements occur during sleep and abruptly stop when the baby is awakened. It generally goes away with age. 

Other conditions with slightly different symptoms also may affect the legs and disrupt sleep. These include restless legs syndrome, periodic limb movements of sleep, night starts (hypnic jerks), and nocturnal leg cramps. They may need further evaluation and treatment (except for night starts).

Can Nocturnal Myoclonus Be Treated?

If nocturnal myoclonus is disruptive to sleep, it may be treated with tetrabenazine, a drug often used to treat movement disorders such as Huntington’s disease. In one study, the condition was significantly improved over a period of five years using this drug, with drowsiness as the most significant side effect.

In most cases, however, treatment is not necessary if sleep is relatively normal. It is believed to be a benign condition, meaning that it has no short-term or long-term impacts on health or well-being for the affected individual.

A Word from Verywell

If you're suffering from sleep myoclonus or have a child or other family member who is, visit a health care provider for further evaluation. Although the condition often resolves on its own, a doctor's visit might put your mind at ease and help you rule out other conditions that might be causing the problems you're experiencing, such as restless leg syndrome.

As with any medical condition, the sooner you get treatment, the sooner you can begin taking control of your symptoms.

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Article Sources
  • Coulter, DL et al. "Benign neonatal sleep myoclonus." Arch Neurol 1982; 39:191.