Myoclonus is a brief twitching of the muscles that can occur separately or in groups, as well as in a sequence or at random. A common form of myoclonus while awake is hiccups, which are quick contractions affecting the diaphragm. Sleep myoclonus, is a form of myoclonus which occurs during sleep, usually in the stage just before deep sleep. Also known as a hypnic jerk or hypnagogic jerk, sleep myoclonus will rarely disturb the subject or bed partner to the point of waking and disrupting sleep patterns.
Sleep myoclonus may be a sign of other nervous system disorders including Parkinson’s disease, Alzheimer’s, multiple sclerosis, and epilepsy. Even though myoclonus can be common in individuals, it may indicate the presence of sleep disorders such as restless legs syndrome and Periodic Leg Movement during Sleep (PLMS).
Myoclonus, especially sleep myoclonus, is not harmful or life threatening, though some of the more complex forms of myoclonus may indicate the presence of other potential nervous system issues, as previously mentioned.
Sleep myoclonus primarily affects the fingers, toes, lips, and eyes, and is often barely perceptible to anyone watching the person in their sleep. Sleep myoclonus has been shown to have some connection to stimulus-sensitive myoclonus, whereby contractions may be caused or increased by environmental factors such as light, sound, or movement.
Myoclonus has been connected to several areas of the brain. In many cases, stimulus-sensitive myoclonus is an overreaction of the brain in the areas that control movement in response to startling events. Myoclonus is actually fairly common in individuals.
Myoclonus on its own does not necessarily require any treatment, but if someone with myoclonus is exhibiting unaccountable symptoms of insomnia, it may be necessary to look into it further. The first step should be to rule out any other sleeping disorders that could be causing the problem by taking an overnight sleep study. The polysomnogram will not only detect any other possible sleeping disorders, but may also indicate whether the myoclonus itself is causing restless sleep.
Treatment for myoclonus is centered on medications which relax the muscles and inhibit contraction. Clonazepam is a commonly issued drug for sleep myoclonus, and when taken near bedtime has the added benefit of causing drowsiness. For this reason it should only be taken before bed, and not as a cure for myoclonus during waking hours. The body may also develop a tolerance for the drug and lessen its usefulness, so the more sparingly it is used, the greater the length of time it will remain useful. Sodium valproate can be used separately or in conjunction with clonazepam to treat myoclonus as well.
Other treatments may also improve other nervous system disorders that may be present during sleep in addition to myoclonus. These include barbiturates, phenytoin, and primidone.
© 2021 American Sleep Association.