Hypnic jerk

Causes

According to the American Academy of Sleep Medicine (AASM), there is a wide range of potential causes, including anxiety, stimulants like caffeine and nicotine, stress, and strenuous activities in the evening. It also may be facilitated by fatigue or sleep deprivation. However, most hypnic jerks occur essentially at random in healthy people. Nevertheless, these repeated, intensifying twitches can cause anxiety in some individuals and a disruption to their sleep onset.

Sometimes, hypnic jerks are mistaken for another form of movement during sleep. For example, hypnic jerks can be confused with restless leg syndrome, periodic limb movement disorder, hypnagogic foot tremor, rhythmic movement disorder, and hereditary or essential startle syndrome. But some phenomena can help to distinguish hypnic jerk from these other conditions. For example, the occurrence of hypnic jerk arises only at sleep onset and it happens without any rhythmicity or periodicity of the movements and EMG bursts. Other pertinent history can also be used to differentiate it.

This physiological phenomenon can also be mistaken for myoclonic seizure, but it can also be distinguished by different criteria such as the fact that hypnic jerk occurs at sleep onset only or that the EEG is normal and constant. In addition, unlike seizures, there are no tongue bites, urinary incontinence, or postictal confusion in hypnic jerk. This phenomenon can therefore be distinguished from other more serious conditions.

The causes of hypnic jerk are unclear and are being studied. None of the several theories that have attempted to explain it have been fully accepted. One hypothesis posits that the hypnic jerk is a form of reflex, initiated in response to normal bodily events during the lead-up to the first stages of sleep, including a decrease in blood pressure and the relaxation of muscle tissue. Another theory postulates that the body mistakes the sense of relaxation that is felt when falling asleep as a sign that the body is physically falling. As a consequence, it causes a jerk motion to wake the sleeper up so they can catch themselves. A researcher at the University of Colorado suggested that a hypnic jerk could be "an archaic reflex to the brain's misinterpretation of muscle relaxation with the onset of sleep as a signal that a sleeping primate is falling out of a tree. The reflex may also have had selective value by having the sleeper readjust or review his or her sleeping position in a nest or on a branch in order to assure that a fall did not occur", but evidence is lacking.

During an epilepsy and intensive care study, the lack of a preceding spike discharge measured on an epilepsy monitoring unit, along with the presence only at sleep onset, helped differentiate hypnic jerks from epileptic myoclonus.

According to a study on sleep disturbances in the Journal of Neural Transmission, a hypnic jerk occurs during the non-rapid eye movement sleep cycle and is an "abrupt muscle action flexing movement, generalized or partial and asymmetric, which may cause arousal, with an illusion of falling". Hypnic jerks are more frequent in childhood with 4 to 7 per hour in the age range from 8 to 12 years old, and they decrease toward 1 or 2 per hour by 65 to 80 years old.

Treatment

There are ways to reduce hypnic jerks, including reducing consumption of stimulants such as nicotine or caffeine, avoiding physical exertion prior to sleep, and consuming sufficient magnesium.

Some medication can also help to reduce or eliminate the hypnic jerks. For example, low-dose clonazepam at bedtime may make the twitches disappear over time.

In addition, some people may develop a fixation on these hypnic jerks, leading to increased anxiety about the disruptive experience. This increased anxiety and fatigue increases the likelihood of experiencing these jerks, resulting in a positive feedback loop.

References

References

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