Shaking before falling asleep: myoclonic spasms

It is three in the evening. You wake up suddenly, practically jumping in your bed, feeling like you are falling from an eight-story building. You notice how your guts still react with a little panic.

Your partner wakes you up at three in the morning, slightly surprised and upset. This tells you that while you were sleeping you kicked him several times. These two small fragments reflect the existence of a phenomenon that occurs very frequently in most of the population: the execution of small, sudden and involuntary movements during sleep.

These movements are called nocturnal myoclonic spasms.

What is myoclonus?

When we talk about myoclonic spasms, we are talking about a series of sudden, brief, completely involuntary muscle contractions that cause the body or part of it to move. They are usually caused by sudden muscle contractions or muscle relaxation.

While these types of spasms can be found in certain disorders such as epilepsy, there are also so-called benign myoclonus. These are generally not considered pathological, being considered normal in people without associated pathology. In fact, a phenomenon as common as hiccups would be a valid example of a benign miaclonic spasm.

These spasms can appear both awake and during sleep, with this article focusing on the latter.

Nocturnal myoclonic spasms

Although the general definition of myoclonus reflects the type of phenomenon in question, those that occur during sleep have a peculiarity: as with hypnagogic and hypnopomic hallucinations, they occur in an altered state of consciousness: sleep or transition between it and awakening. Miaclonic spasms would in this case be a type of parasomnia, Episodic phenomena or disorders occurring during sleep and characterized by the presence of vegetative or motor symptoms.

It is a generally non-pathological phenomenon with a high prevalence in the population. It is estimated that approximately 70% of the population has experienced a myoclonic spasm at some point during sleep. However, if the symptoms occur repeatedly and consistently, it would be advisable to see a doctor, as if they occur persistently, it could indicate the presence of a disorder.

It should be noted that it is possible to confuse this type of disorder, which is not dangerous, with an epileptic seizure. In this aspect, one of the few ways to differentiate is by means of the electroencephalogram, by not assuming the myoclonic spasms the same type of alterations as those seen in epilepsy.

Neurological causes of myoclonic spasms during sleep

The reason why these spasms occur during sleep has a neuroscientific explanation.

The appearance of nocturnal myoclonus is due to the presence of a lack of coordination, at the same time maintaining the activity, of two specific brain areas. Specifically, the reticular formation or the reticular activation system (SAR) and the ventrolateral preoptic nucleus.

Reticular activation system

This system located in the brainstem is primarily responsible for keeping us alive, as it is the brain system that directs unconscious processes such as breathing, digestion, or heart rate. Apart from these physiological processes, it also participates in the maintenance of vigilance and the concentration of attention, in the maintenance of the waking state.

Ventrolateral preoptic nucleus

The ventrolateral preoptic nucleus is found in the anterior hypothalamus, near and in contact with the occipital lobe. This nucleus is responsible for “turning off consciousness” by inducing the state of sleep, as well as protecting the body during sleep by causing bodily paralysis that prevents us from moving and damaging during deep sleep.

When myoclonic spasms occur

To understand the appearance of spasms it is necessary to consider that although during sleep this reduces its operation, the SAR does not stop its operation (since this would cause the death of the one who is affected).

Thus, this system still has some activation which can sometimes contradict the functioning during sleep of the ventrolateral preoptic nucleus which induces sleep.

This contradiction, the cause of which is still unknown, it may partially cause motor reactions typical of waking up during sleep. In other words, it is the cause of myoclonic spasms during sleep.

Types of nocturnal myoclonus

Myoclonic spasms during sleep they are not uniform and homogeneous, but there are three basic types.

A first type is found in repetitive movements during sleep. Similar to the movements typical of epileptic seizures, these movements appear during non-REM sleep, being repetitive movements of short duration. Although it does not usually require treatment, the very severe forms can be treated pharmacologically.

A second type of presenting myoclonic spasm during sleep is nocturnal twitching or startle myoclonus. The clearest example of this type of spasm is the typical movement that occurs when you wake up from a dream in which you have the feeling of falling. They usually occur in superficial sleep, that is to say in the first two phases of sleep, causing those who suffer from it to wake up with a certain brutality. Usually these are massive shaking of the whole body, especially the lower extremities.

Finally, some spasms can be found at the time of the transition between wakefulness and sleep. This type of myoclonus, classified as non-specific, acts on the muscles of the face and limbs.

Bibliographical references:

  • Ferber, R. and Kryger, M. (1995). Principles and practice of sleep medicine in children. WBSaunders Company.
  • Besag, FMC (1995). Myoclonus and infantile spasms. In: Robertson MM, Eapen V, eds. Allied movement and childhood troubles. Chichester: John Wiley and Sons, Ltd .; p. 149-76.
  • Fejerman, N .; Medina, CS and Caraballo, RN (1997). Paroxysmal disorders and non-epileptic episodic symptoms. In: Fejerman N, Fernández-Álvarez E, eds. Pediatric neurology. 2nd ed. Madrid: Editorial Mèdica Panamericana SA; p. 584-99.
  • Fernández-Álvarez, E. and Aicardi, J. (2001). Movement disorders in childhood. London: Mac Keith Press.
  • Morairty, S .; Rainnie, D .; McCarley, R. and Greene, R. (2004). Disinhibition of active sleep neurons in the ventrolateral preoptic zone by adenosine: a new mechanism for promoting sleep. Neurosciences; 123: 451-7
  • Svorad, D. (1957). “Brainstem Reticular Activation System and Animal Hypnosis.” Science 125 (3239): 156-156.

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