What Is Sleep Myoclonus?

Sudden Jerking or Muscle Spasms During Sleep

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

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If you have ever seen your infant suddenly jerk during sleep, it may give you a start or causes you to worry. What you are seeing is likely a benign condition known as sleep myoclonus, also known as nocturnal myoclonus. While myoclonus tends to resolve spontaneously over time in babies, it can suddenly develop in adults for any number of reasons.

Symptoms

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 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.

Sleep myoclonus occurs during the early stages of sleep, especially at the moment of dropping off to sleep, and may either be incidental or provoked by external stimuli such as noise, movement, or light.

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.

PLMD 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. 

Causes

Although the cause is not clear, sleep myoclonus may involve problems with a neurotransmitter called dopamine. This distinction alone differentiates it from seizures, which involve electrical changes in the brain.

Myoclonus also may be a side effect to some drugs, including levodopa, cyclic antidepressants, and bismuth salts. The condition often improves once the drug is stopped.

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.

Sleep Myoclonus in Children

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.

Sleep myoclonus is common during the first week of a newborn's life and usually resolves within a year. Commonly referred to as benign neonatal sleep myoclonus, there are no inherent consequences to the condition or reasons for concern.

Infants who experience sleep myoclonus will have a normal neurologic examination and electroencephalogram (EEG). If these movements occur during wakefulness, further evaluation by your child's doctor may be needed to rule out seizures and other causes.

Treatment

Sleep myoclonus is not considered serious or in need of treatment unless it is interfering with sleep and a person's quality of life.

If it is, the condition may be treated with Xenazine (tetrabenazine), a drug often used to treat movement disorders such as Huntington’s disease. In one study, Xenazine significantly improved symptoms of severe myoclonus over five years, with only drowsiness being a notable side effect.

Xenazine should not be used in people with abnormally low blood pressure, depression, suicidal thoughts, Parkinson's disease, liver disease, or uncontrolled heart rhythm disorders.

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.