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Have you ever been jerked out of sleep by a sudden twitch or uncontrolled muscle movement, or noticed jerks and twitches in your sleep partner? You are not alone, since these movements during sleep occur in up to 70 percent of people. They are commonly called sleep starts or hypnic jerks. [1,2] The medical term is sleep myoclonus. [2,3]
Sleep myoclonus is just one type of myoclonus. An example of a myoclonus that occurs when you are awake is hiccups. Sleep myoclonus and hiccups are called physiologic types of myoclonus, that means that they happen in healthy people. Other types of myoclonus – called pathologic myoclonus – may be severe enough to prevent you from eating, talking, or walking. 
Symptoms of Sleep Myoclonus
The cause of sleep myoclonus is not known. In some cases, it may be an overreaction of your brain and spinal cord to light, noise, or movement that occurs as you are dropping off to sleep.  The brief twitches and jerks of sleep myoclonus commonly involve your lips, toes, fingers, and eyes. These movements do not wake you or your sleep partner.  Sleep myoclonus can also cause a sensation of falling as you drift off to sleep. You may have uncontrollable movements of your arms, legs, or body. These movements may wake you or your sleep partner. 
Treatment and Prevention of Sleep Myoclonus
In most cases, sleep myoclonus does not require any treatment. You may be at higher risk if you drink caffeine or exercise later in the day. Other risk factors are emotional stress and being sleep deprived. You may be able to prevent sleep myoclonus by avoiding these risk factors. Because sleep myoclonus may be triggered by noise, light, or movement, sleeping in a dark quiet room may also help. [1-3]
If uncontrolled movements during sleep are strong enough to wake you, or keep you from getting enough sleep, talk to your doctor. These sleep movements may be a warning for a disease like Parkinson’s disease, MS, Alzheimer’s disease, or epilepsy. Uncontrollable sleep movements may also be a sign of two common sleep disorders called restless legs syndrome (RLS) and periodic leg movement of sleep (PLMS). These disorders should be diagnosed and treated, because they are much more likely to seriously disturb your sleep. [1-3]
RLS: An Irresistible Urge to Move your Legs
RLS can occur while you are awake or asleep. It causes an uncomfortable and uncontrollable urge to move your legs. It usually occurs in both legs and rarely in the arms. People describe the sensation as throbbing, crawling, pulling, and creeping. Moving gives temporary relief. Symptoms are usually worse when you are lying in bed and can keep your from sleeping or falling asleep. People may complain of daytime sleepiness, mood changes, and trouble concentrating from lack of sleep.
RLS is common. It may occur in up to 10 percent of people. It is more common in women and it increases with age. The cause is not known. You may be at higher risk if you:
- Have a family history of RLS
- Have kidney disease
- Have iron deficiency
- Take a medication for nausea, seizures, schizophrenia, depression, or allergy
- Drink alcohol, smoke, or drink caffeine
- Are pregnant
- Have sleep apnea or are sleep deprived for any reason 
RLS is usually diagnosed by the symptoms. Treatment may include correcting an underlying problem like kidney disease, iron deficiency, or sleep apnea. Lifestyle changes like exercise and avoiding nicotine, alcohol, and caffeine may help. Several medications are also used. There is no cure but symptoms can usually be controlled. It is important to know that over 80 percent of people with RLS also have PLMS. 
PLMS: Involuntary Movements of Your Legs During Sleep
PLMS happens during sleep. It is more common than RLS and may occur in up to 50 percent of people over age 50. PLMS can cause mild leg movements that do not wake you up, or they can cause severe movements that wake you and your sleep partner. Like sleep myoclonus, mild PLMS does not require treatment. If PLMS is severe enough to cause loss of sleep, daytime sleepiness, mood changes, and irritability it is called periodic limb movement disorder (PLMD). 
Symptoms of PLMS are uncontrolled movements of both legs. Like RLS, movement occurs soon after falling asleep. Movement tends to occur in the early stage of sleep. They start in your toes and move to the ankles, knees, and hips. These movements may occur every 5 to 90 seconds and last from 30 minutes to 2 hours during sleep. In rare cases, there may also be arm movements. 
The cause of PLMS is not known, but is probably the same as RLS. Risk factors for PLMS are similar to RLS and the treatments are also similar. One difference is that you can have PLMS without knowing it. Unless you have a sleep partner to tell you about it, you may only complain of daytime sleepiness, mood changes, or trouble concentrating. You may need a sleep study to get diagnosed. 
The Importance of Sleep Hygiene
For sleep myoclonus, RLS, and PLMS, sleep hygiene is an important part of treatment and prevention. Sleep hygiene is a combination of lifestyle changes that you can make to assure yourself a full and restful sleep. They are good sleep habits. They include:
- Going to bed and waking up at the same time every day, including on weekends and vacations
- Getting seven hours of sleep every night
- Avoiding the TV, computer, and phone before bed and keeping the TV and computer out of your your bedroom
- Keeping your bedroom quiet, dark, and comfortable
- Establishing a relaxing bedtime routine
- Avoiding bright lights, caffeine, alcohol, large meals, and lots of fluids later in the evening and before bed.
- Eating a healthy diet and exercising regularly 
Types of Myoclonus
Under the umbrella term “myoclonus”—the condition that causes jerking or twitching while sleeping—there are a number of forms. The causes and effects for each are different, and responses to each can vary widely. According to the National Institute of Neurological Disorders and Stroke (NINDS), these are the most commonly described:
1. Action myoclonus
“Characterized by muscular jerking triggered or intensified by voluntary movement or even the intention to move,” the NINDS reports. “Action myoclonus is the most disabling form of myoclonus and can affect the arms, legs, face, and even the voice. This type of myoclonus often is caused by brain damage that results from a lack of oxygen and blood flow to the brain when breathing or heartbeat is temporarily stopped.”
2. Cortical reflex myoclonus
May be a type of epilepsy, one that originates in the cerebral cortex. “In this type of myoclonus, jerks usually involve only a few muscles in one part of the body, but jerks involving many muscles also may occur.”
3. Essential myoclonus
Tends to be “stable without increasing in severity over time,” the NINDS says, adding that essential myoclonus “occurs in the absence of epilepsy or other apparent abnormalities in the brain or nerves.” It may be an inherited disorder but can also crop up randomly in people with no family history.
4. Palatal myoclonus
Occurs in one or both sides of the rear of the roof of the mouth (the soft palate) as regular, rhythmic contractions. Palatal myoclonus contractions may be accompanied by twitching in other muscles, including those in the face, tongue, throat, and diaphragm. “The contractions are very rapid, occurring as often as 150 times a minute,” the NINDS explains, “and may persist during sleep. The condition usually appears in adults and can last indefinitely.” It can appear as “clicking” sounds, and can also cause severe pain in some people.
5. Progressive myoclonus epilepsy (PME)
Refers to a group of diseases characterized by myoclonus, epileptic seizures, and other serious symptoms (difficultly speaking or walking, for example). “These rare disorders often get worse over time,” the NNDS reports, “and sometimes are fatal.” PME has been linked to an abnormality in the gene that codes for the protein cystitis B, which regulates enzymes that break down other proteins.
6. Reticular reflex myoclonus
Believed to be a form of generalized epilepsy originating in the brain stem, which connects to the spinal cord and controls such vital functions as our heartbeat and our breathing. Voluntary movement or external stimuli can trigger reticular reflex myoclonus.
7. Stimulus-sensitive myoclonus
A variety of sources—light, noise, movement—can trigger this form of myoclonus.
8. Sleep myoclonus
Can occur during the first phases of sleep, and can be stimulus-sensitive. Sleep myoclonus may not require treatment for some, but myoclonus “may be a symptom in more complex and disturbing sleep disorders, such as restless legs syndrome,” the NINDS says. If so, it may require treatment by your healthcare provider.
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- American Sleep Association, What is Sleep Myoclonus?
- National Sleep Foundation, Hypnic Jerks: Why Do They Happen?
- NIH, Myoclonus Fact Sheet
- NIH, Restless Leg Syndrome fact Sheet
- American Sleep Association, Periodic Leg Movements During Sleep (PLMS) & Periodic Limb Movement Disorder (PLMD)
- American Academy of Sleep Medicine, Healthy Sleep Habits