Sleep myoclonus is a form of myoclonus which occurs during sleep, usually in the stage just before deep sleep. Sleep myoclonus will rarely disturb the subject or any bed partner to the point of waking and disrupting sleep, but may indicate the presence or future development of more serious sleep related disorders such as restless legs syndrome and periodic limb movement.
Myoclonus is a brief twitching of the muscles, and can occur separately or in groups, as well as in a sequence or at random. Myoclonus is a leading sign of other nervous system disorders including Parkinson’s disease, Alzheimer’s, multiple sclerosis and epilepsy. Myoclonus is caused by sudden jerks or contractions in the muscles, and also of the muscles uncontracting or relaxing after contraction. The most common form of myoclonus is hiccups, which are quick contractions affecting the diaphragm. Myoclonus, especially sleep myoclonus in particular, are not harmful or life threatening, though some of the more complex forms of myoclonus may indicate the presence of other potentially life threatening nervous system diseases.
Sleep myoclonus primarily affects the fingers, toes, lips and eyes, and is often barely perceptible to anyone watching the person in their sleep. It does not cause involuntary limb movement. 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 highly tied to several areas of the brain, and in many cases stimulus-sensitive myoclonus has been shown to be an overreaction of the brain in areas that control movement in response to startling events.
Myoclonus is common in individuals, but is only responsible for about 5% of insomnia related cases. The presence of myoclonus may indicate one or more other sleeping disorders are present as well, including sleep apnea, narcolepsy and other movement disorders. It is most commonly found in adult males.
Myoclonus on its own will not likely require any method of 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 tranquilizers, 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. The complex nature of myoclonus often requires several drugs to treat effectively, and to this end several other treatments that target multiple areas of the brain which may be affecting myoclonus are also in development or not yet fully tested.